Spring Cloud provides tools for developers to quickly build some of +the common patterns in distributed systems (e.g. configuration +management, service discovery, circuit breakers, intelligent routing, +micro-proxy, control bus, one-time tokens, global locks, leadership +election, distributed sessions, cluster state). Coordination of +distributed systems leads to boiler plate patterns, and using Spring +Cloud developers can quickly stand up services and applications that +implement those patterns. They will work well in any distributed +environment, including the developer’s own laptop, bare metal data +centres, and managed platforms such as Cloud Foundry.
+Features
+Spring Cloud focuses on providing good out of box experience for typical use cases +and extensibility mechanism to cover others.
+-
+
-
+
Distributed/versioned configuration
+
+ -
+
Service registration and discovery
+
+ -
+
Routing
+
+ -
+
Service-to-service calls
+
+ -
+
Load balancing
+
+ -
+
Circuit Breakers
+
+ -
+
Global locks
+
+ -
+
Leadership election and cluster state
+
+ -
+
Distributed messaging
+
+
Cloud Native Applications
+Cloud Native is a style of application development that encourages easy adoption of best practices in the areas of continuous delivery and value-driven development. A related discipline is that of building 12-factor Apps in which development practices are aligned with delivery and operations goals, for instance by using declarative programming and management and monitoring. Spring Cloud facilitates these styles of development in a number of specific ways and the starting point is a set of features that all components in a distributed system either need or need easy access to when required.
+Many of those features are covered by Spring Boot, which we build on in Spring Cloud. Some more are delivered by Spring Cloud as two libraries: Spring Cloud Context and Spring Cloud Commons. Spring Cloud Context provides utilities and special services for the ApplicationContext of a Spring Cloud application (bootstrap context, encryption, refresh scope and environment endpoints). Spring Cloud Commons is a set of abstractions and common classes used in different Spring Cloud implementations (eg. Spring Cloud Netflix vs. Spring Cloud Consul).
If you are getting an exception due to "Illegal key size" and you are using Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:
+-
+
- + + +
- + + +
- + + +
Extract files into JDK/jre/lib/security folder (whichever version of JRE/JDK x64/x86 you are using).
+|
+ Note
+ |
++Spring Cloud is released under the non-restrictive Apache 2.0 license. If you would like to contribute to this section of the documentation or if you find an error, please find the source code and issue trackers in the project at github. + | +
Spring Cloud Context: Application Context Services
+Spring Boot has an opinionated view of how to build an application +with Spring: for instance it has conventional locations for common +configuration file, and endpoints for common management and monitoring +tasks. Spring Cloud builds on top of that and adds a few features that +probably all components in a system would use or occasionally need.
+The Bootstrap Application Context
+A Spring Cloud application operates by creating a "bootstrap"
+context, which is a parent context for the main application. Out of
+the box it is responsible for loading configuration properties from
+the external sources, and also decrypting properties in the local
+external configuration files. The two contexts share an Environment
+which is the source of external properties for any Spring
+application. Bootstrap properties are added with high precedence, so
+they cannot be overridden by local configuration.
The bootstrap context uses a different convention for locating
+external configuration than the main application context, so instead
+of application.yml (or .properties) you use bootstrap.yml,
+keeping the external configuration for bootstrap and main context
+nicely separate. Example:
spring:
+ application:
+ name: foo
+ cloud:
+ config:
+ uri: ${SPRING_CONFIG_URI:http://localhost:8888}
+It is a good idea to set the spring.application.name (in
+bootstrap.yml or application.yml) if your application needs any
+application-specific configuration from the server.
You can disable the bootstrap process completely by setting
+spring.cloud.bootstrap.enabled=false (e.g. in System properties).
Application Context Hierarchies
+If you build an application context from SpringApplication or
+SpringApplicationBuilder, then the Bootstrap context is added as a
+parent to that context. It is a feature of Spring that child contexts
+inherit property sources and profiles from their parent, so the "main"
+application context will contain additional property sources, compared
+to building the same context without Spring Cloud Config. The
+additional property sources are:
-
+
-
+
"bootstrap": an optional
+CompositePropertySourceappears with high +priority if anyPropertySourceLocatorsare found in the Bootstrap +context, and they have non-empty properties. An example would be +properties from the Spring Cloud Config Server. See +below for instructions +on how to customize the contents of this property source.
+ -
+
"applicationConfig: [classpath:bootstrap.yml]" (and friends if +Spring profiles are active). If you have a
+bootstrap.yml(or +properties) then those properties are used to configure the Bootstrap +context, and then they get added to the child context when its parent +is set. They have lower precedence than theapplication.yml(or +properties) and any other property sources that are added to the child +as a normal part of the process of creating a Spring Boot +application. See below for +instructions on how to customize the contents of these property +sources.
+
Because of the ordering rules of property sources the "bootstrap"
+entries take precedence, but note that these do not contain any data
+from bootstrap.yml, which has very low precedence, but can be used
+to set defaults.
You can extend the context hierarchy by simply setting the parent
+context of any ApplicationContext you create, e.g. using its own
+interface, or with the SpringApplicationBuilder convenience methods
+(parent(), child() and sibling()). The bootstrap context will be
+the parent of the most senior ancestor that you create yourself.
+Every context in the hierarchy will have its own "bootstrap" property
+source (possibly empty) to avoid promoting values inadvertently from
+parents down to their descendants. Every context in the hierarchy can
+also (in principle) have a different spring.application.name and
+hence a different remote property source if there is a Config
+Server. Normal Spring application context behaviour rules apply to
+property resolution: properties from a child context override those in
+the parent, by name and also by property source name (if the child has
+a property source with the same name as the parent, the one from the
+parent is not included in the child).
Note that the SpringApplicationBuilder allows you to share an
+Environment amongst the whole hierarchy, but that is not the
+default. Thus, sibling contexts in particular do not need to have the
+same profiles or property sources, even though they will share common
+things with their parent.
Changing the Location of Bootstrap Properties
+The bootstrap.yml (or .properties) location can be specified using
+spring.cloud.bootstrap.name (default "bootstrap") or
+spring.cloud.bootstrap.location (default empty), e.g. in System
+properties. Those properties behave like the spring.config.*
+variants with the same name, in fact they are used to set up the
+bootstrap ApplicationContext by setting those properties in its
+Environment. If there is an active profile (from
+spring.profiles.active or through the Environment API in the
+context you are building) then properties in that profile will be
+loaded as well, just like in a regular Spring Boot app, e.g. from
+bootstrap-development.properties for a "development" profile.
Customizing the Bootstrap Configuration
+The bootstrap context can be trained to do anything you like by adding
+entries to /META-INF/spring.factories under the key
+org.springframework.cloud.bootstrap.BootstrapConfiguration. This is
+a comma-separated list of Spring @Configuration classes which will
+be used to create the context. Any beans that you want to be available
+to the main application context for autowiring can be created here,
+and also there is a special contract for @Beans of type
+ApplicationContextInitializer. Classes can be marked with an @Order
+if you want to control the startup sequence (the default order is
+"last").
|
+ Warning
+ |
+
+Be careful when adding custom BootstrapConfiguration that the
+classes you add are not @ComponentScanned by mistake into your
+"main" application context, where they might not be needed.
+Use a separate package name for boot configuration classes that is
+not already covered by your @ComponentScan or @SpringBootApplication
+annotated configuration classes.
+ |
+
The bootstrap process ends by injecting initializers into the main
+SpringApplication instance (i.e. the normal Spring Boot startup
+sequence, whether it is running as a standalone app or deployed in an
+application server). First a bootstrap context is created from the
+classes found in spring.factories and then all @Beans of type
+ApplicationContextInitializer are added to the main
+SpringApplication before it is started.
Customizing the Bootstrap Property Sources
+The default property source for external configuration added by the
+bootstrap process is the Config Server, but you can add additional
+sources by adding beans of type PropertySourceLocator to the
+bootstrap context (via spring.factories). You could use this to
+insert additional properties from a different server, or from a
+database, for instance.
As an example, consider the following trivial custom locator:
+@Configuration
+public class CustomPropertySourceLocator implements PropertySourceLocator {
+
+ @Override
+ public PropertySource<?> locate(Environment environment) {
+ return new MapPropertySource("customProperty",
+ Collections.<String, Object>singletonMap("property.from.sample.custom.source", "worked as intended"));
+ }
+
+}The Environment that is passed in is the one for the
+ApplicationContext about to be created, i.e. the one that we are
+supplying additional property sources for. It will already have its
+normal Spring Boot-provided property sources, so you can use those to
+locate a property source specific to this Environment (e.g. by
+keying it on the spring.application.name, as is done in the default
+Config Server property source locator).
If you create a jar with this class in it and then add a
+META-INF/spring.factories containing:
org.springframework.cloud.bootstrap.BootstrapConfiguration=sample.custom.CustomPropertySourceLocator+
then the "customProperty" PropertySource will show up in any
+application that includes that jar on its classpath.
Environment Changes
+The application will listen for an EnvironmentChangedEvent and react
+to the change in a couple of standard ways (additional
+ApplicationListeners can be added as @Beans by the user in the
+normal way). When an EnvironmentChangedEvent is observed it will
+have a list of key values that have changed, and the application will
+use those to:
-
+
-
+
Re-bind any
+@ConfigurationPropertiesbeans in the context
+ -
+
Set the logger levels for any properties in
+logging.level.*
+
Note that the Config Client does not by default poll for changes in
+the Environment, and generally we would not recommend that approach
+for detecting changes (although you could set it up with a
+@Scheduled annotation). If you have a scaled-out client application
+then it is better to broadcast the EnvironmentChangedEvent to all
+the instances instead of having them polling for changes (e.g. using
+the Spring Cloud
+Bus).
The EnvironmentChangedEvent covers a large class of refresh use
+cases, as long as you can actually make a change to the Environment
+and publish the event (those APIs are public and part of core
+Spring). You can verify the changes are bound to
+@ConfigurationProperties beans by visiting the /configprops
+endpoint (normal Spring Boot Actuator feature). For instance a
+DataSource can have its maxPoolSize changed at runtime (the
+default DataSource created by Spring Boot is an
+@ConfigurationProperties bean) and grow capacity
+dynamically. Re-binding @ConfigurationProperties does not cover
+another large class of use cases, where you need more control over the
+refresh, and where you need a change to be atomic over the whole
+ApplicationContext. To address those concerns we have
+@RefreshScope.
Refresh Scope
+A Spring @Bean that is marked as @RefreshScope will get special
+treatment when there is a configuration change. This addresses the
+problem of stateful beans that only get their configuration injected
+when they are initialized. For instance if a DataSource has open
+connections when the database URL is changed via the Environment, we
+probably want the holders of those connections to be able to complete
+what they are doing. Then the next time someone borrows a connection
+from the pool he gets one with the new URL.
Refresh scope beans are lazy proxies that initialize when they are +used (i.e. when a method is called), and the scope acts as a cache of +initialized values. To force a bean to re-initialize on the next +method call you just need to invalidate its cache entry.
+The RefreshScope is a bean in the context and it has a public method
+refreshAll() to refresh all beans in the scope by clearing the
+target cache. There is also a refresh(String) method to refresh an
+individual bean by name. This functionality is exposed in the
+/refresh endpoint (over HTTP or JMX).
|
+ Note
+ |
+
+@RefreshScope works (technically) on an @Configuration
+class, but it might lead to surprising behaviour: e.g. it does not
+mean that all the @Beans defined in that class are themselves
+@RefreshScope. Specifically, anything that depends on those beans
+cannot rely on them being updated when a refresh is initiated, unless
+it is itself in @RefreshScope (in which it will be rebuilt on a
+refresh and its dependencies re-injected, at which point they will be
+re-initialized from the refreshed @Configuration).
+ |
+
Encryption and Decryption
+The Config Client has an Environment pre-processor for decrypting
+property values locally. It follows the same rules as the Config
+Server, and has the same external configuration via encrypt.*. Thus
+you can use encrypted values in the form {cipher}* and as long as
+there is a valid key then they will be decrypted before the main
+application context gets the Environment. To use the encryption
+features in a client you need to include Spring Security RSA in your
+classpath (Maven co-ordinates
+"org.springframework.security:spring-security-rsa") and you also need
+the full strength JCE extensions in your JVM.
If you are getting an exception due to "Illegal key size" and you are using Sun’s JDK, you need to install the Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files. See the following links for more information:
+-
+
- + + +
- + + +
- + + +
Extract files into JDK/jre/lib/security folder (whichever version of JRE/JDK x64/x86 you are using).
+Endpoints
+For a Spring Boot Actuator application there are some additional management endpoints:
+-
+
-
+
POST to
+/envto update theEnvironmentand rebind@ConfigurationPropertiesand log levels
+ -
+
+/refreshfor re-loading the boot strap context and refreshing the@RefreshScopebeans
+ -
+
+/restartfor closing theApplicationContextand restarting it (disabled by default)
+ -
+
+/pauseand/resumefor calling theLifecyclemethods (stop()andstart()on theApplicationContext)
+
Spring Cloud Commons: Common Abstractions
+Patterns such as service discovery, load balancing and circuit breakers lend themselves to a common abstraction layer that can be consumed by all Spring Cloud clients, independent of the implementation (e.g. discovery via Eureka or Consul).
+Spring RestTemplate as a Load Balancer Client
+You can use Ribbon indirectly via an autoconfigured RestTemplate
+when RestTemplate is on the classpath and a LoadBalancerClient bean is defined):
public class MyClass {
+ @Autowired
+ private RestTemplate restTemplate;
+
+ public String doOtherStuff() {
+ String results = restTemplate.getForObject("http://stores/stores", String.class);
+ return results;
+ }
+}The URI needs to use a virtual host name (ie. service name, not a host name).
+The Ribbon client is used to create a full physical address. See
+RibbonAutoConfiguration
+for details of how the RestTemplate is set up.
Multiple RestTemplate objects
+If you want a RestTemplate that is not load balanced, create a RestTemplate
+bean and inject it as normal. To access the load balanced RestTemplate use
+the provided `@LoadBalanced Qualifier:
public class MyClass {
+ @Autowired
+ private RestTemplate restTemplate;
+
+ @Autowired
+ @LoadBalanced
+ private RestTemplate loadBalanced;
+
+ public String doOtherStuff() {
+ return loadBalanced.getForObject("http://stores/stores", String.class);
+ }
+
+ public String doStuff() {
+ return restTemplate.getForObject("http://example.com", String.class);
+ }
+}Ignore Network Interfaces
+Sometimes it is useful to ignore certain named network interfaces so they can be excluded from Service Discovery registration (eg. running in a Docker container). A list of regular expressions can be set that will cause the desired network interfaces to be ignored. The following configuration will ignore the "docker0" interface and all interfaces that start with "veth".
+spring: + cloud: + inetutils: + ignoredInterfaces: + - docker0 + - veth.*+
Spring Cloud Config
+Environment and PropertySource abstractions, so they fit very well with Spring applications, but can be used with any application running in any language. As an application moves through the deployment pipeline from dev to test and into production you can manage the configuration between those environments and be certain that applications have everything they need to run when they migrate. The default implementation of the server storage backend uses git so it easily supports labelled versions of configuration environments, as well as being accessible to a wide range of tooling for managing the content. It is easy to add alternative implementations and plug them in with Spring configuration.
+Quick Start
+Start the server:
+$ cd spring-cloud-config-server +$ mvn spring-boot:run+
The server is a Spring Boot application so you can run it from your
+IDE instead if you prefer (the main class is
+ConfigServerApplication). Then try it out a client:
$ curl localhost:8888/foo/development
+{"name":"development","label":"master","propertySources":[
+ {"name":"https://github.com/scratches/config-repo/foo-development.properties","source":{"bar":"spam"}},
+ {"name":"https://github.com/scratches/config-repo/foo.properties","source":{"foo":"bar"}}
+]}
+The default strategy for locating property sources is to clone a git
+repository (at spring.cloud.config.server.git.uri) and use it to
+initialize a mini SpringApplication. The mini-application’s
+Environment is used to enumerate property sources and publish them
+via a JSON endpoint.
The HTTP service has resources in the form:
+/{application}/{profile}[/{label}]
+/{application}-{profile}.yml
+/{label}/{application}-{profile}.yml
+/{application}-{profile}.properties
+/{label}/{application}-{profile}.properties
+where the "application" is injected as the spring.config.name in the
+SpringApplication (i.e. what is normally "application" in a regular
+Spring Boot app), "profile" is an active profile (or comma-separated
+list of properties), and "label" is an optional git label (defaults to
+"master".)
The YAML and properties forms are coalesced into a single +map, even if the origin of the values (reflected in the +"propertySources" of the "standard" form) has multiple sources.
+Spring Cloud Config Server pulls configuration for remote clients +from a git repository (which must be provided):
+spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repoClient Side Usage
+To use these features in an application, just build it as a Spring
+Boot application that depends on spring-cloud-config-client (e.g. see
+the test cases for the config-client, or the sample app). The most
+convenient way to add the dependency is via a Spring Boot starter
+org.springframework.cloud:spring-cloud-starter-config. There is also a
+parent pom and BOM (spring-cloud-starter-parent) for Maven users and a
+Spring IO version management properties file for Gradle and Spring CLI
+users. Example Maven configuration:
<parent>
+ <groupId>org.springframework.boot</groupId>
+ <artifactId>spring-boot-starter-parent</artifactId>
+ <version>1.2.3.RELEASE</version>
+ <relativePath /> <!-- lookup parent from repository -->
+</parent>
+
+<dependencyManagement>
+ <dependencies>
+ <dependency>
+ <groupId>org.springframework.cloud</groupId>
+ <artifactId>spring-cloud-starter-parent</artifactId>
+ <version>1.0.1.RELEASE</version>
+ <type>pom</type>
+ <scope>import</scope>
+ </dependency>
+ </dependencies>
+</dependencyManagement>
+
+<dependencies>
+ <dependency>
+ <groupId>org.springframework.cloud</groupId>
+ <artifactId>spring-cloud-starter-config</artifactId>
+ </dependency>
+ <dependency>
+ <groupId>org.springframework.boot</groupId>
+ <artifactId>spring-boot-starter-test</artifactId>
+ <scope>test</scope>
+ </dependency>
+</dependencies>
+
+<build>
+ <plugins>
+ <plugin>
+ <groupId>org.springframework.boot</groupId>
+ <artifactId>spring-boot-maven-plugin</artifactId>
+ </plugin>
+ </plugins>
+</build>
+
+<!-- repositories also needed for snapshots and milestones -->Then you can create a standard Spring Boot application, like this simple HTTP server:
+@SpringBootApplication
+@RestController
+public class Application {
+
+ @RequestMapping("/")
+ public String home() {
+ return "Hello World!";
+ }
+
+ public static void main(String[] args) {
+ SpringApplication.run(Application.class, args);
+ }
+
+}
+When it runs it will pick up the external configuration from the
+default local config server on port 8888 if it is running. To modify
+the startup behaviour you can change the location of the config server
+using bootstrap.properties (like application.properties but for
+the bootstrap phase of an application context), e.g.
spring.cloud.config.uri: http://myconfigserver.com+
The bootstrap properties will show up in the /env endpoint as a
+high-priority property source, e.g.
$ curl localhost:8080/env
+{
+ "profiles":[],
+ "configService:https://github.com/spring-cloud-samples/config-repo/bar.properties":{"foo":"bar"},
+ "servletContextInitParams":{},
+ "systemProperties":{...},
+ ...
+}
+(a property source called "configService:<URL of remote +repository>/<file name>" contains the property "foo" with value +"bar" and is highest priority).
+|
+ Note
+ |
++the URL in the property source name is the git repository not +the config server URL. + | +
Spring Cloud Config Server
+The Server provides an HTTP, resource-based API for external
+configuration (name-value pairs, or equivalent YAML content). The
+server is easily embeddable in a Spring Boot application using the
+@EnableConfigServer annotation. So this app is a config server:
@SpringBootApplication
+@EnableConfigServer
+public class ConfigServer {
+ public static void main(String[] args) {
+ SpringApplication.run(ConfigServer.class, args);
+ }
+}Like all Spring Boot apps it runs on port 8080 by default, but you
+can switch it to the conventional port 8888 in various ways. The
+easiest, which also sets a default configuration repository,
+is by launching it with spring.config.name=configserver (there
+is a configserver.yml in the Config Server jar). Another is
+to use your own application.properties, e.g.
server.port: 8888
+spring.cloud.config.server.git.uri: file://${user.home}/config-repowhere ${user.home}/config-repo is a git repository containing
+YAML and properties files.
|
+ Note
+ |
+
+in Windows you need an extra "/" in the file URL if it is
+absolute with a drive prefix, e.g. file:///${user.home}/config-repo.
+ |
+
|
+ Tip
+ |
+
+
+
+Here’s a recipe for creating the git repository in the example +above: +
+
+
+
+$ cd $HOME +$ mkdir config-repo +$ cd config-repo +$ git init . +$ echo info.foo: bar > application.properties +$ git add -A . +$ git commit -m "Add application.properties"+ |
+
|
+ Warning
+ |
++using the local filesystem for your git repository is +intended for testing only. Use a server to host your +configuration repositories in production. + | +
Environment Repository
+Where do you want to store the configuration data for the Config
+Server? The strategy that governs this behaviour is the
+EnvironmentRepository, serving Environment objects. This
+Environment is a shallow copy of the domain from the Spring
+Environment (including propertySources as the main feature). The
+Environment resources are parametrized by three variables:
-
+
-
+
+{application}maps to "spring.application.name" on the client side;
+ -
+
+{profile}maps to "spring.active.profiles" on the client (comma separated list); and
+ -
+
+{label}which is a server side feature labelling a "versioned" set of config files.
+
Repository implementations generally behave just like a Spring Boot
+application loading configuration files from a "spring.config.name"
+equal to the {application} parameter, and "spring.profiles.active"
+equal to the {profiles} parameter. Precedence rules for profiles are
+also the same as in a regular Boot application: active profiles take
+precedence over defaults, and if there are multiple profiles the last
+one wins (like adding entries to a Map).
Example: a client application has this bootstrap configuration:
+spring:
+ application:
+ name: foo
+ profiles:
+ active: dev,mysql(as usual with a Spring Boot application, these properties could also +be set as environment variables or command line arguments).
+If the repository is file-based, the server will create an
+Environment from application.yml (shared between all clients), and
+foo.yml (with foo.yml taking precedence). If the YAML files have
+documents inside them that point to Spring profiles, those are applied
+with higher precendence (in order of the profiles listed), and if
+there are profile-specific YAML (or properties) files these are also
+applied with higher precedence than the defaults. Higher precendence
+translates to a PropertySource listed earlier in the
+Environment. (These are the same rules as apply in a standalone
+Spring Boot application.)
Git Backend
+The default implementation of EnvironmentRepository uses a Git
+backend, which is very convenient for managing upgrades and physical
+environments, and also for auditing changes. To change the location of
+the repository you can set the "spring.cloud.config.server.git.uri"
+configuration property in the Config Server (e.g. in
+application.yml). If you set it with a file: prefix it should work
+from a local repository so you can get started quickly and easily
+without a server, but in that case the server operates directly on the
+local repository without cloning it (it doesn’t matter if it’s not
+bare because the Config Server never makes changes to the "remote"
+repository). To scale the Config Server up and make it highly
+available, you would need to have all instances of the server pointing
+to the same repository, so only a shared file system would work. Even
+in that case it is better to use the ssh: protocol for a shared
+filesystem repository, so that the server can clone it and use a local
+working copy as a cache.
This repository implementation maps the {label} parameter of the
+HTTP resource to a git label (commit id, branch name or tag). If the
+git branch or tag name contains a slash ("/") then the label in the
+HTTP URL should be specified with the special string "(_)" instead (to
+avoid ambiguity with other URL paths). Be careful with the brackets in
+the URL if you are using a command line client like curl (e.g. escape
+them from the shell with quotes '').
Placeholders in Git URI
+Spring Cloud Config Server supports a git repository URL with
+placeholders for the {application} and {profile} (and {label} if
+you need it, but remember that the label is applied as a git label
+anyway). So you can easily support a "one repo per application" policy
+using (for example):
spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/myorg/{application}or a "one repo per profile" policy using a similar pattern but with
+{profile}.
Pattern Matching and Multiple Repositories
+There is also support for more complex requirements with pattern
+matching on the application and profile name. The pattern format is a
+comma-separated list of {application}/{profile} names with wildcards
+(where a pattern beginning with a wildcard may need to be
+quoted). Example:
spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repo
+ repos:
+ simple: https://github.com/simple/config-repo
+ special:
+ pattern: special*/dev*,*special*/dev*
+ uri: https://github.com/special/config-repo
+ local:
+ pattern: local*
+ uri: file:/home/configsvc/config-repoIf {application}/{profile} does not match any of the patterns, it
+will use the default uri defined under
+"spring.cloud.config.server.git.uri". In the above example, for the
+"simple" repository, the pattern is simple/* (i.e. it only matches
+one application named "simple" in all profiles). The "local"
+repository matches all application names beginning with "local" in all
+profiles (the /* suffix is added automatically to any pattern that
+doesn’t have a profile matcher).
|
+ Note
+ |
++the "one-liner" short cut used in the "simple" example above can +only be used if the only property to be set is the URI. If you need to +set anything else (credentials, pattern, etc.) you need to use the full +form. + | +
The pattern property in the repo is actually an array, so you can
+use a YAML array (or [0], [1], etc. suffixes in properties files)
+to bind to multiple patterns. You may need to do this if you are going
+to run apps with multiple profiles. Example:
spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repo
+ repos:
+ development:
+ pattern:
+ - */development
+ - */staging
+ uri: https://github.com/development/config-repo
+ staging:
+ pattern:
+ - */qa
+ - */production
+ uri: https://github.com/staging/config-repo|
+ Note
+ |
+
+Spring Cloud will guess that a pattern containing a profile that
+doesn’t end in * implies that you actually want to match a list of
+profiles starting with this pattern (so */staging is a shortcut for
+["*/staging", "*/staging,*"]). This is common where you need to run
+apps in the "development" profile locally but also the "cloud" profile
+remotely, for instance.
+ |
+
Every repository can also optionally store config files in
+sub-directories, and patterns to search for those directories can be
+specified as searchPaths. For example at the top level:
spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repo
+ searchPaths: foo,bar*In this example the server searches for config files in the top level +and in the "foo/" sub-directory and also any sub-directory whose name +begins with "bar".
+By default the server clones remote repositories when configuration +is first requested. The server can be configured to clone the repositories +at startup. For example at the top level:
+spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://git/common/config-repo.git
+ repos:
+ team-a:
+ pattern: team-a-*
+ cloneOnStart: true
+ uri: http://git/team-a/config-repo.git
+ team-b:
+ pattern: team-b-*
+ cloneOnStart: false
+ uri: http://git/team-b/config-repo.git
+ team-c:
+ pattern: team-c-*
+ uri: http://git/team-a/config-repo.gitIn this example the server clones team-a’s config-repo on startup before it +accepts any requests. All other repositories will not be cloned until +configuration from the repository is requested.
+To use HTTP basic authentication on the remote repository add the +"username" and "password" properties separately (not in the URL), +e.g.
+spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repo
+ username: trolley
+ password: strongpasswordIf you don’t use HTTPS and user credentials, SSH should also work out
+of the box when you store keys in the default directories (~/.ssh)
+and the uri points to an SSH location,
+e.g. "git@github.com:configuration/cloud-configuration". The
+repository is accessed using JGit, so any documentation you find on
+that should be applicable. HTTPS proxy settings can be set in
+~/.git/config or in the same way as for any other JVM process via
+system properties (-Dhttps.proxyHost and -Dhttps.proxyPort).
Placeholders in Git Search Paths
+Spring Cloud Config Server also supports a search path with
+placeholders for the {application} and {profile} (and {label} if
+you need it). Example:
spring:
+ cloud:
+ config:
+ server:
+ git:
+ uri: https://github.com/spring-cloud-samples/config-repo
+ searchPaths: {application}searches the repository for files in the same name as the directory +(as well as the top level). Wildcards are also valid in a search +path with placeholders (any matching directory is included in the +search).
+File System Backend
+There is also a "native" profile in the Config Server that doesn’t use +Git, but just loads the config files from the local classpath or file +system (any static URL you want to point to with +"spring.cloud.config.server.native.searchLocations"). To use the +native profile just launch the Config Server with +"spring.profiles.active=native".
+|
+ Note
+ |
+
+Remember to use the file: prefix for file resources (the
+default without a prefix is usually the classpath). Just as with any
+Spring Boot configuration you can embed ${}-style environment
+placeholders, but remember that absolute paths in Windows require an
+extra "/", e.g. file:///${user.home}/config-repo
+ |
+
|
+ Warning
+ |
+
+The default value of the searchLocations is identical to a
+local Spring Boot application (so [classpath:/, classpath:/config,
+file:./, file:./config]). This does not expose the
+application.properties from the server to all clients because any
+property sources present in the server are removed before being sent
+to the client.
+ |
+
|
+ Tip
+ |
++A filesystem backend is great for getting started quickly and +for testing. To use it in production you need to be sure that the +file system is reliable, and shared across all instances of the +Config Server. + | +
The search locations can contain placeholders for {application},
+{profile} and {label}. In this way you can segregate the
+directories in the path, and choose a strategy that makes sense for
+you (e.g. sub-directory per application, or sub-directory per
+profile).
If you don’t use placeholders in the search locations, this repository
+also appends the {label} parameter of the HTTP resource to a suffix
+on the search path, so properties files are loaded from each search
+location and a subdirectory with the same name as the label (the
+labelled properties take precedence in the Spring Environment). Thus
+the default behaviour with no placeholders is the same as adding a
+search location ending with /{label}/. For example `file:/tmp/config
+is the same as file:/tmp/config,file:/tmp/config/{label}
Sharing Configiration With All Applications
+With file-based (i.e. git, svn and native) repositories, resources
+with file names in application* are shared between all client
+applications (so application.properties, application.yml,
+application-*.properties etc.). You can use resources with these
+file names to configure global defaults and have them overridden by
+application-specific files as necessary.
The #_property_overrides[property overrides] feature can also be used +for setting global defaults, and with placeholders applications are +allowed to override them locally.
+|
+ Tip
+ |
+
+With the "native" profile (local file system backend) it is
+recommended that you use an explicit search location that isn’t part
+of the server’s own configuration. Otherwise the application*
+resources in the default search locations are removed because they are
+part of the server.
+ |
+
Property Overrides
+The Config Server has an "overrides" feature that allows the operator
+to provide configuration properties to all applications that cannot be
+accidentally changed by the application using the normal Spring Boot
+hooks. To declare overrides just add a map of name-value pairs to
+spring.cloud.config.server.overrides. For example
spring:
+ cloud:
+ config:
+ server:
+ overrides:
+ foo: barwill cause all applications that are config clients to read foo=bar
+independent of their own configuration. (Of course an application can
+use the data in the Config Server in any way it likes, so overrides
+are not enforceable, but they do provide useful default behaviour if
+they are Spring Cloud Config clients.)
|
+ Tip
+ |
+
+Normal, Spring environment placeholders with "${}" can be escaped
+(and resolved on the client) by using backslash ("\") to escape the
+"$" or the "{", e.g. \${app.foo:bar} resolves to "bar" unless the
+app provides its own "app.foo". Note that in YAML you don’t need to
+escape the backslash itself, but in properties files you do, when you
+configure the overrides on the server.
+ |
+
You can change the priority of all overrides in the client to be more +like default values, allowing applications to supply their own values +in environment variables or System properties, by setting the flag `
+Health Indicator
+Config Server comes with a Health Indicator that checks if the configured
+EnvironmentRepository is working. By default it asks the EnvironmentRepository
+for an application named app, the default profile and the default
+label provided by the EnvironmentRepository implementation.
You can configure the Health Indicator to check more applications +along with custom profiles and custom labels, e.g.
+spring:
+ cloud:
+ config:
+ server:
+ health:
+ repositories:
+ myservice:
+ label: mylabel
+ myservice-dev:
+ name: myservice
+ profiles: developmentYou can disable the Health Indicator by setting spring.cloud.config.server.health.enabled=false.
Security
+You are free to secure your Config Server in any way that makes sense +to you (from physical network security to OAuth2 bearer +tokens), and Spring Security and Spring Boot make it easy to do pretty +much anything.
+To use the default Spring Boot configured HTTP Basic security, just
+include Spring Security on the classpath (e.g. through
+spring-boot-starter-security). The default is a username of "user"
+and a randomly generated password, which isn’t going to be very useful
+in practice, so we recommend you configure the password (via
+security.user.password) and encrypt it (see below for instructions
+on how to do that).
Encryption and Decryption
+|
+ Important
+ |
++Prerequisites: to use the encryption and decryption features +you need the full-strength JCE installed in your JVM (it’s not there by default). +You can download the "Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files" +from Oracle, and follow instructions for installation (essentially replace the 2 policy files +in the JRE lib/security directory with the ones that you downloaded). + | +
If the remote property sources contain encrypted content (values
+starting with {cipher}) they will be decrypted before sending to
+clients over HTTP. The main advantage of this set up is that the
+property values don’t have to be in plain text when they are "at rest"
+(e.g. in a git repository). If a value cannot be decrypted it is
+removed from the property source and an additional property is added
+with the same key, but prefixed with "invalid." and a value that means
+"not applicable" (usually "<n/a>"). This is largely to prevent cipher
+text being used as a password and accidentally leaking.
If you are setting up a remote config repository for config client
+applications it might contain an application.yml like this, for
+instance:
spring:
+ datasource:
+ username: dbuser
+ password: '{cipher}FKSAJDFGYOS8F7GLHAKERGFHLSAJ'Encrypted values in a .properties file must not be wrapped in quotes, otherwise the value will not be decrypted:
+spring.datasource.username: dbuser
+spring.datasource.password: {cipher}FKSAJDFGYOS8F7GLHAKERGFHLSAJ
+You can safely push this plain text to a shared git repository and the +secret password is protected.
+The server also exposes /encrypt and /decrypt endpoints (on the
+assumption that these will be secured and only accessed by authorized
+agents). If you are editing a remote config file you can use the Config Server
+to encrypt values by POSTing to the /encrypt endpoint, e.g.
$ curl localhost:8888/encrypt -d mysecret +682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda+
The inverse operation is also available via /decrypt (provided the server is
+configured with a symmetric key or a full key pair):
$ curl localhost:8888/decrypt -d 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda +mysecret+
|
+ Tip
+ |
+
+If you are testing like this with curl, then use
+--data-urlencode (instead of -d) or set an explicit Content-Type:
+text/plain to make sure curl encodes the data correctly when there
+are special characters ('+' is particularly tricky).
+ |
+
Take the encrypted value and add the {cipher} prefix before you put
+it in the YAML or properties file, and before you commit and push it
+to a remote, potentially insecure store.
The /encrypt and /decrypt endpoints also both accept paths of the
+form /*/{name}/{profiles} which can be used to control cryptography
+per application (name) and profile when clients call into the main
+Environment resource.
|
+ Note
+ |
+
+to control the cryptography in this granular way you must also
+provide a @Bean of type TextEncryptorLocator that creates a
+different encryptor per name and profiles. The one that is provided
+by default does not do this (so all encryptions use the same key).
+ |
+
The spring command line client (with Spring Cloud CLI extensions
+installed) can also be used to encrypt and decrypt, e.g.
$ spring encrypt mysecret --key foo +682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda +$ spring decrypt --key foo 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda +mysecret+
To use a key in a file (e.g. an RSA public key for encryption) prepend +the key value with "@" and provide the file path, e.g.
+$ spring encrypt mysecret --key @${HOME}/.ssh/id_rsa.pub
+AQAjPgt3eFZQXwt8tsHAVv/QHiY5sI2dRcR+...
+The key argument is mandatory (despite having a -- prefix).
Key Management
+The Config Server can use a symmetric (shared) key or an asymmetric +one (RSA key pair). The asymmetric choice is superior in terms of +security, but it is often more convenient to use a symmetric key since +it is just a single property value to configure.
+To configure a symmetric key you just need to set encrypt.key to a
+secret String (or use an enviroment variable ENCRYPT_KEY to keep it
+out of plain text configuration files).
To configure an asymmetric key you can either set the key as a
+PEM-encoded text value (in encrypt.key), or via a keystore (e.g. as
+created by the keytool utility that comes with the JDK). The
+keystore properties are encrypt.keyStore.* with * equal to
-
+
-
+
+location(aResourcelocation),
+ -
+
+password(to unlock the keystore) and
+ -
+
+alias(to identify which key in the store is to be +used).
+
The encryption is done with the public key, and a private key is +needed for decryption. Thus in principle you can configure only the +public key in the server if you only want to do encryption (and are +prepared to decrypt the values yourself locally with the private +key). In practice you might not want to do that because it spreads the +key management process around all the clients, instead of +concentrating it in the server. On the other hand it’s a useful option +if your config server really is relatively insecure and only a +handful of clients need the encrypted properties.
+Creating a Key Store for Testing
+To create a keystore for testing you can do something like this:
+$ keytool -genkeypair -alias mytestkey -keyalg RSA \ + -dname "CN=Web Server,OU=Unit,O=Organization,L=City,S=State,C=US" \ + -keypass changeme -keystore server.jks -storepass letmein+
Put the server.jks file in the classpath (for instance) and then in
+your application.yml for the Config Server:
encrypt:
+ keyStore:
+ location: classpath:/server.jks
+ password: letmein
+ alias: mytestkey
+ secret: changemeUsing Multiple Keys and Key Rotation
+In addition to the {cipher} prefix in encrypted property values, the
+Config Server looks for {name:value} prefixes (zero or many) before
+the start of the (Base64 encoded) cipher text. The keys are passed to
+a TextEncryptorLocator which can do whatever logic it needs to
+locate a TextEncryptor for the cipher. If you have configured a
+keystore (encrypt.keystore.location) the default locator will look
+for keys in the store with aliases as supplied by the "key" prefix,
+i.e. with a cipher text like this:
foo:
+ bar: `{cipher}{key:testkey}...`the locator will look for a key named "testkey". A secret can also be
+supplied via a {secret:…} value in the prefix, but if it is not
+the default is to use the keystore password (which is what you get
+when you build a keytore and don’t specify a secret). If you do
+supply a secret it is recommended that you also encrypt the secrets
+using a custom SecretLocator.
Key rotation is hardly ever necessary on cryptographic grounds if the
+keys are only being used to encrypt a few bytes of configuration data
+(i.e. they are not being used elsewhere), but occasionally you might
+need to change the keys if there is a security breach for instance. In
+that case all the clients would need to change their source config
+files (e.g. in git) and use a new {key:…} prefix in all the
+ciphers, checking beforehand of course that the key alias is available
+in the Config Server keystore.
|
+ Tip
+ |
+
+the {name:value} prefixes can also be added to plaintext posted
+to the /encrypt endpoint, if you want to let the Config Server
+handle all encryption as well as decryption.
+ |
+
Serving Plain Text
+Instead of using the Environment abstraction (or one of the
+alternative representations of it in YAML or properties format) your
+applications might need generic plain text configuration files,
+tailored to their environment. The Config Server provides these
+through an additional endpoint at /{name}/{profile}/{label}/{path}
+where "name", "profile" and "label" have the same meaning as the
+regular environment endpoint, but "path" is a file name
+(e.g. log.xml). The source files for this endpoint are located in
+the same way as for the environment endpoints: the same search path is
+used as for properties or YAML files, but instead of aggregating all
+matching resources, only the first one to match is returned.
After a resource is located, placeholders in the normal format
+(${…}) are resolved using the effective Environment for the
+application name, profile and label supplied. In this way the resource
+endpoint is tightly integrated with the environment
+endpoints. Example, if you have this layout for a GIT (or SVN)
+repository:
application.yml +nginx.conf+
where nginx.conf looks like this:
server {
+ listen 80;
+ server_name ${nginx.server.name};
+}
+and application.yml like this:
nginx:
+ server:
+ name: example.com
+---
+spring:
+ profiles: development
+nginx:
+ server:
+ name: develop.comthen the /foo/default/master/nginx.conf resource looks like this:
server {
+ listen 80;
+ server_name example.com;
+}
+and /foo/development/master/nginx.conf like this:
server {
+ listen 80;
+ server_name develop.com;
+}
+|
+ Note
+ |
+
+just like the source files for environment configuration, the
+"profile" is used to resolve the file name, so if you want a
+profile-specific file then /*/development/*/logback.xml will be
+resolved by a file called logback-development.xml (in preference
+to logback.xml).
+ |
+
Embedding the Config Server
+The Config Server runs best as a standalone application, but if you
+need to you can embed it in another application. Just use the
+@EnableConfigServer annotation. An optional property that can be
+useful in this case is spring.cloud.config.server.bootstrap which is
+a flag to indicate that the server should configure itself from its
+own remote repository. The flag is off by default because it can delay
+startup, but when embedded in another application it makes sense to
+initialize the same way as any other application.
|
+ Note
+ |
+
+It should be obvious, but remember that if you use the bootstrap
+flag the config server will need to have its name and repository URI
+configured in bootstrap.yml.
+ |
+
To change the location of the server endpoints you can (optionally)
+set spring.cloud.config.server.prefix, e.g. "/config", to serve the
+resources under a prefix. The prefix should start but not end with a
+"/". It is applied to the @RequestMappings in the Config Server
+(i.e. underneath the Spring Boot prefixes server.servletPath and
+server.contextPath).
If you want to read the configuration for an application directly from
+the backend repository (instead of from the config server) that’s
+basically an embedded config server with no endpoints. You can switch
+off the endpoints entirely if you don’t use the @EnableConfigServer
+annotation (just set spring.cloud.config.server.bootstrap=true).
Push Notifications and Spring Cloud Bus
+Many source code repository providers (like Github, Gitlab or Bitbucket
+for instance) will notify you of changes in a repository through a
+webhook. You can configure the webhook via the provider’s user
+interface as a URL and a set of events in which you are
+interested. For instance
+Github
+will POST to the webhook with a JSON body containing a list of
+commits, and a header "X-Github-Event" equal to "push". If you add a
+dependency on the spring-cloud-config-monitor library and activate
+the Spring Cloud Bus in your Config Server, then a "/monitor" endpoint
+is enabled.
When the webhook is activated the Config Server will send a
+RefreshRemoteApplicationEvent targeted at the applications it thinks
+might have changed. The change detection can be strategized, but by
+default it just looks for changes in files that match the application
+name (e.g. "foo.properties" is targeted at the "foo" application, and
+"application.properties" is targeted at all applications). The strategy
+if you want to override the behaviour is PropertyPathNotificationExtractor
+which accepts the request headers and body as parameters and returns a list
+of file paths that changed.
The default configuration works out of the box with Github, Gitlab or
+Bitbucket. In addition to the JSON notifications from Github, Gitlab
+or Bitbucket you can trigger a change notification by POSTing to
+"/monitor" with a form-encoded body parameters path={name}. This will
+broadcast to applications matching the "{name}" pattern (can contain
+wildcards).
|
+ Note
+ |
+
+the RefreshRemoteApplicationEvent will only be transmitted if
+the spring-cloud-bus is activated in the Config Server and in the
+client application.
+ |
+
|
+ Note
+ |
++the default configuration also detects filesystem changes in +local git repositories (the webhook is not used in that case but as +soon as you edit a config file a refresh will be broadcast). + | +
Spring Cloud Config Client
+A Spring Boot application can take immediate advantage of the Spring
+Config Server (or other external property sources provided by the
+application developer), and it will also pick up some additional
+useful features related to Environment change events.
Config First Bootstrap
+This is the default behaviour for any application which has the Spring
+Cloud Config Client on the classpath. When a config client starts up
+it binds to the Config Server (via the bootstrap configuration
+property spring.cloud.config.uri) and initializes Spring
+Environment with remote property sources.
The net result of this is that all client apps that want to consume
+the Config Server need a bootstrap.yml (or an environment variable)
+with the server address in spring.cloud.config.uri (defaults to
+"http://localhost:8888").
Eureka First Bootstrap
+If you are using Spring Cloud Netflix and Eureka Service Discovery, +then you can have the Config Server register with Eureka if you want +to, but in the default "Config First" mode, clients won’t be able to +take advantage of the registration.
+If you prefer to use Eureka to locate the Config Server, you can do
+that by setting spring.cloud.config.discovery.enabled=true (default
+"false"). The net result of that is that client apps all need a
+bootstrap.yml (or an environment variable) with the Eureka server
+address, e.g. in eureka.client.serviceUrl.defaultZone. The price
+for using this option is an extra network round trip on start up to
+locate the service registration. The benefit is that the Config Server
+can change its co-ordinates, as long as Eureka is a fixed point. The
+default service id is "CONFIGSERVER" but you can change that on the
+client with spring.cloud.config.discovery.serviceId (and on the server
+in the usual way for a service, e.g. by setting spring.application.name).
The discovery client implementations all support some kind of metadata
+map (e.g. for Eureka we have eureka.instance.metadataMap). Some
+additional properties of the Config Server may need to be configured
+in its service registration metadata so that clients can connect
+correctly. If the Config Server is secured with HTTP Basic you can
+configure the credentials as "username" and "password". And if the
+Config Server has a context path you can set "configPath". Example,
+for a Config Server that is a Eureka client:
eureka:
+ instance:
+ ...
+ metadataMap:
+ username: osufhalskjrtl
+ password: lviuhlszvaorhvlo5847
+ configPath: /configConfig Client Fail Fast
+In some cases, it may be desirable to fail startup of a service if
+it cannot connect to the Config Server. If this is the desired
+behavior, set the bootstrap configuration property
+spring.cloud.config.failFast=true and the client will halt with
+an Exception.
Config Client Retry
+If you expect that the config server may occasionally be unavailable when
+your app starts, you can ask it to keep trying after a failure. First you need
+to set spring.cloud.config.failFast=true, and then you need to add
+spring-retry and spring-boot-starter-aop to your classpath. The default
+behaviour is to retry 6 times with an initial backoff interval of 1000ms and an
+exponential multiplier of 1.1 for subsequent backoffs. You can configure these
+properties (and others) using spring.cloud.config.retry.* configuration properties.
|
+ Tip
+ |
+
+To take full control of the retry add a @Bean of type
+RetryOperationsInterceptor with id "configServerRetryInterceptor". Spring
+Retry has a RetryInterceptorBuilder that makes it easy to create one.
+ |
+
Locating Remote Configuration Resources
+The Config Service serves property sources from /{name}/{profile}/{label}, where the default bindings in the client app are
-
+
-
+
"name" =
+${spring.application.name}
+ -
+
"profile" =
+${spring.profiles.active}(actuallyEnvironment.getActiveProfiles())
+ -
+
"label" = "master"
+
+
All of them can be overridden by setting spring.cloud.config.*
+(where * is "name", "profile" or "label"). The "label" is useful for
+rolling back to previous versions of configuration; with the default
+Config Server implementation it can be a git label, branch name or
+commit id. Label can also be provided as a comma-separated list, in
+which case the items in the list are tried on-by-one until one succeeds.
+This can be useful when working on a feature branch, for instance,
+when you might want to align the config label with your branch, but
+make it optional (e.g. spring.cloud.config.label=myfeature,develop).
Security
+If you use HTTP Basic security on the server then clients just need to +know the password (and username if it isn’t the default). You can do +that via the config server URI, or via separate username and password +properties, e.g.
+spring:
+ cloud:
+ config:
+ uri: https://user:secret@myconfig.mycompany.comor
+spring:
+ cloud:
+ config:
+ uri: https://myconfig.mycompany.com
+ username: user
+ password: secretThe spring.cloud.config.password and spring.cloud.config.username
+values override anything that is provided in the URI.
If you deploy your apps on Cloud Foundry then the best way to provide +the password is through service credentials, e.g. in the URI, since +then it doesn’t even need to be in a config file. An example which +works locally and for a user-provided service on Cloud Foundry named +"configserver":
+spring:
+ cloud:
+ config:
+ uri: ${vcap.services.configserver.credentials.uri:http://user:password@localhost:8888}If you use another form of security you might need to provide a
+RestTemplate to the ConfigServicePropertySourceLocator (e.g. by
+grabbing it in the bootstrap context and injecting one).
Spring Cloud Netflix
+Service Discovery: Eureka Clients
+Service Discovery is one of the key tenets of a microservice based architecture. Trying to hand configure each client or some form of convention can be very difficult to do and can be very brittle. Eureka is the Netflix Service Discovery Server and Client. The server can be configured and deployed to be highly available, with each server replicating state about the registered services to the others.
+Registering with Eureka
+When a client registers with Eureka, it provides meta-data about itself +such as host and port, health indicator URL, home page etc. Eureka +receives heartbeat messages from each instance belonging to a service. +If the heartbeat fails over a configurable timetable, the instance is +normally removed from the registry.
+Example eureka client:
+@Configuration
+@ComponentScan
+@EnableAutoConfiguration
+@EnableEurekaClient
+@RestController
+public class Application {
+
+ @RequestMapping("/")
+ public String home() {
+ return "Hello world";
+ }
+
+ public static void main(String[] args) {
+ new SpringApplicationBuilder(Application.class).web(true).run(args);
+ }
+
+}(i.e. utterly normal Spring Boot app). In this example we use
+@EnableEurekaClient explicitly, but with only Eureka available you
+could also use @EnableDiscoveryClient. Configuration is required to
+locate the Eureka server. Example:
eureka: + client: + serviceUrl: + defaultZone: http://localhost:8761/eureka/+
where "defaultZone" is a magic string fallback value that provides the +service URL for any client that doesn’t express a preference +(i.e. it’s a useful default).
+The default application name (service ID), virtual host and non-secure
+port, taken from the Environment, are ${spring.application.name},
+${spring.application.name} and ${server.port} respectively.
@EnableEurekaClient makes the app into both a Eureka "instance"
+(i.e. it registers itself) and a "client" (i.e. it can query the
+registry to locate other services). The instance behaviour is driven
+by eureka.instance.* configuration keys, but the defaults will be
+fine if you ensure that your application has a
+spring.application.name (this is the default for the Eureka service
+ID, or VIP).
See EurekaInstanceConfigBean and EurekaClientConfigBean for more details of the configurable options.
+Status Page and Health Indicator
+The status page and health indicators for a Eureka instance default to
+"/info" and "/health" respectively, which are the default locations of
+useful endpoints in a Spring Boot Actuator application. You need to
+change these, even for an Actuator application if you use a
+non-default context path or servlet path
+(e.g. server.servletPath=/foo) or management endpoint path
+(e.g. management.contextPath=/admin). Example:
eureka:
+ instance:
+ statusPageUrlPath: ${management.context-path}/info
+ healthCheckUrlPath: ${management.context-path}/health
+These links show up in the metadata that is consumed by clients, and +used in some scenarios to decide whether to send requests to your +application, so it’s helpful if they are accurate.
+Registering a Secure Application
+If your app wants to be contacted over HTTPS you can set two flags in
+the EurekaInstanceConfig, viz
+eureka.instance.[nonSecurePortEnabled,securePortEnabled]=[false,true]
+respectively. This will make Eureka publish instance information
+showing an explicit preference for secure communication. The Spring
+Cloud DiscoveryClient will always return an https://…; URI for a
+service configured this way, and the Eureka (native) instance
+information will have a secure health check URL.
Because of the way +Eureka works internally, it will still publish a non-secure URL for +status and home page unless you also override those explicitly. +You can use placeholders to configure the eureka instance urls, +e.g.
+eureka:
+ instance:
+ statusPageUrl: https://${eureka.hostname}/info
+ healthCheckUrl: https://${eureka.hostname}/health
+ homePageUrl: https://${eureka.hostname}/
+(Note that ${eureka.hostname} is a native placeholder only available
+in later versions of Eureka. You could achieve the same thing with
+Spring placeholders as well, e.g. using ${eureka.instance.hostName}.)
|
+ Note
+ |
++If your app is running behind a proxy, and the SSL termination +is in the proxy (e.g. if you run in Cloud Foundry or other platforms +as a service) then you will need to ensure that the proxy "forwarded" +headers are intercepted and handled by the application. An embedded +Tomcat container in a Spring Boot app does this automatically if it +has explicit configuration for the 'X-Forwarded-\*` headers. A sign +that you got this wrong will be that the links rendered by your app to +itself will be wrong (the wrong host, port or protocol). + | +
Eureka’s Health Checks
+By default, Eureka uses the client heartbeat to determine if a client is up. +Unless specified otherwise the Discovery Client will not propagate the +current health check status of the application per the Spring Boot Actuator. Which means +that after successful registration Eureka will always announce that the +application is in 'UP' state. This behaviour can be altered by enabling +Eureka health checks, which results in propagating application status +to Eureka. As a consequence every other application won’t be sending +traffic to application in state other then 'UP'.
+eureka: + client: + healthcheck: + enabled: true+
If you require more control over the health checks, you may consider
+implementing your own com.netflix.appinfo.HealthCheckHandler.
Eureka Metadata for Instances and Clients
+It’s worth spending a bit of time understanding how the Eureka metadata works, so you can use it in a way that makes sense in your platform. There is standard metadata for things like hostname, IP address, port numbers, status page and health check. These are published in the service registry and used by clients to contact the services in a straightforward way. Additional metadata can be added to the instance registration in the eureka.instance.metadataMap, and this will be accessible in the remote clients, but in general will not change the behaviour of the client, unless it is made aware of the meaning of the metadata. There are a couple of special cases described below where Spring Cloud already assigns meaning to the metadata map.
Using Eureka on Cloudfoundry
+Cloudfoundry has a global router so that all instances of the same app have the same hostname (it’s the same in other PaaS solutions with a similar architecture). This isn’t necessarily a barrier to using Eureka, but if you use the router (recommended, or even mandatory depending on the way your platform was set up), you need to explicitly set the hostname and port numbers (secure or non-secure) so that they use the router. You might also want to use instance metadata so you can distinguish between the instances on the client (e.g. in a custom load balancer). By default, the eureka.instance.instanceId is vcap.application.instance_id. For example:
eureka:
+ instance:
+ hostname: ${vcap.application.uris[0]}
+ nonSecurePort: 80
+Depending on the way the security rules are set up in your Cloudfoundry instance, you might be able to register and use the IP address of the host VM for direct service-to-service calls. This feature is not (yet) available on Pivotal Web Services (PWS).
+Using Eureka on AWS
+If the application is planned to be deployed to an AWS cloud, then the Eureka instance will have to be configured to be Amazon aware and this can be done by customizing the EurekaInstanceConfigBean the following way:
+@Bean
+@Profile("!default")
+public EurekaInstanceConfigBean eurekaInstanceConfig() {
+ EurekaInstanceConfigBean b = new EurekaInstanceConfigBean();
+ AmazonInfo info = AmazonInfo.Builder.newBuilder().autoBuild("eureka");
+ b.setDataCenterInfo(info);
+ return b;
+}Changing the Eureka Instance ID
+A vanilla Netflix Eureka instance is registered with an ID that is equal to its host name (i.e. only one service per host). Spring Cloud Eureka provides a sensible default that looks like this: ${spring.cloud.client.hostname}:${spring.application.name}:${spring.application.instance_id:${server.port}}}. For example myhost:myappname:8080.
Using Spring Cloud you can override this by providing a unique identifier in eureka.instance.instanceId. For example:
eureka:
+ instance:
+ instanceId: ${spring.application.name}:${spring.application.instance_id:${random.value}}
+With this metadata, and multiple service instances deployed on
+localhost, the random value will kick in there to make the instance
+unique. In Cloudfoundry the spring.application.instance_id will be
+populated automatically in a Spring Boot Actuator application, so the
+random value will not be needed.
Using the EurekaClient
+Once you have an app that is @EnableDiscoveryClient (or @EnableEurekaClient) you can use it to
+discover service instances from the Eureka Server. One way to do that is to use the native
+com.netflix.discovery.EurekaClient (as opposed to the Spring
+Cloud DiscoveryClient), e.g.
@Autowired
+private EurekaClient discoveryClient;
+
+public String serviceUrl() {
+ InstanceInfo instance = discoveryClient.getNextServerFromEureka("STORES", false);
+ return instance.getHomePageUrl();
+}
+|
+ Tip
+ |
+
+
+
+Don’t use the |
+
Alternatives to the native Netflix EurekaClient
+You don’t have to use the raw Netflix EurekaClient and usually it
+is more convenient to use it behind a wrapper of some sort. Spring
+Cloud has support for Feign (a REST client
+builder) and also Spring RestTemplate using
+the logical Eureka service identifiers (VIPs) instead of physical
+URLs. To configure Ribbon with a fixed list of physical servers you
+can simply set <client>.ribbon.listOfServers to a comma-separated
+list of physical addresses (or hostnames), where <client> is the ID
+of the client.
You can also use the org.springframework.cloud.client.discovery.DiscoveryClient
+which provides a simple API for discovery clients that is not specific
+to Netflix, e.g.
@Autowired
+private DiscoveryClient discoveryClient;
+
+public String serviceUrl() {
+ List<ServiceInstance> list = client.getInstances("STORES");
+ if (list != null && list.size() > 0 ) {
+ return list.get(0).getUri();
+ }
+ return null;
+}
+Why is it so Slow to Register a Service?
+Being an instance also involves a periodic heartbeat to the registry
+(via the client’s serviceUrl) with default duration 30 seconds. A
+service is not available for discovery by clients until the instance,
+the server and the client all have the same metadata in their local
+cache (so it could take 3 hearbeats). You can change the period using
+eureka.instance.leaseRenewalIntervalInSeconds and this will speed up
+the process of getting clients connected to other services. In
+production it’s probably better to stick with the default because
+there are some computations internally in the server that make
+assumptions about the lease renewal period.
Service Discovery: Eureka Server
+Example eureka server (e.g. using spring-cloud-starter-eureka-server to set up the classpath):
+@SpringBootApplication
+@EnableEurekaServer
+public class Application {
+
+ public static void main(String[] args) {
+ new SpringApplicationBuilder(Application.class).web(true).run(args);
+ }
+
+}The server has a home page with a UI, and HTTP API endpoints per the
+normal Eureka functionality under /eureka/*.
Eureka background reading: see flux capacitor and google group discussion.
+|
+ Tip
+ |
+
+
+
+Due to Gradle’s dependency resolution rules and the lack of a parent bom feature, simply depending on spring-cloud-starter-eureka-server can cause failures on application startup. To remedy this the Spring dependency management plugin must be added and the Spring cloud starter parent bom must be imported like so: +
+
+build.gradle
+
+
+ |
+
High Availability, Zones and Regions
+The Eureka server does not have a backend store, but the service +instances in the registry all have to send heartbeats to keep their +registrations up to date (so this can be done in memory). Clients also +have an in-memory cache of eureka registrations (so they don’t have to +go to the registry for every single request to a service).
+By default every Eureka server is also a Eureka client and requires +(at least one) service URL to locate a peer. If you don’t provide it +the service will run and work, but it will shower your logs with a lot +of noise about not being able to register with the peer.
+See also below for details of Ribbon +support on the client side for Zones and Regions.
+Standalone Mode
+The combination of the two caches (client and server) and the +heartbeats make a standalone Eureka server fairly resilient to +failure, as long as there is some sort of monitor or elastic runtime +keeping it alive (e.g. Cloud Foundry). In standalone mode, you might +prefer to switch off the client side behaviour, so it doesn’t keep +trying and failing to reach its peers. Example:
+server:
+ port: 8761
+
+eureka:
+ instance:
+ hostname: localhost
+ client:
+ registerWithEureka: false
+ fetchRegistry: false
+ serviceUrl:
+ defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/
+Notice that the serviceUrl is pointing to the same host as the local
+instance.
Peer Awareness
+Eureka can be made even more resilient and available by running
+multiple instances and asking them to register with each other. In
+fact, this is the default behaviour, so all you need to do to make it
+work is add a valid serviceUrl to a peer, e.g.
--- +spring: + profiles: peer1 +eureka: + instance: + hostname: peer1 + client: + serviceUrl: + defaultZone: http://peer2/eureka/ + +--- +spring: + profiles: peer2 +eureka: + instance: + hostname: peer2 + client: + serviceUrl: + defaultZone: http://peer1/eureka/+
In this example we have a YAML file that can be used to run the same
+server on 2 hosts (peer1 and peer2), by running it in different
+Spring profiles. You could use this configuration to test the peer
+awareness on a single host (there’s not much value in doing that in
+production) by manipulating /etc/hosts to resolve the host names. In
+fact, the eureka.instance.hostname is not needed if you are running
+on a machine that knows its own hostname (it is looked up using
+java.net.InetAddress by default).
You can add multiple peers to a system, and as long as they are all +connected to each other by at least one edge, they will synchronize +the registrations amongst themselves. If the peers are physically +separated (inside a data centre or between multiple data centres) then +the system can in principle survive split-brain type failures.
+Prefer IP Address
+In some cases, it is preferable for Eureka to advertise the IP Adresses
+of services rather than the hostname. Set eureka.instance.preferIpAddress
+to true and when the application registers with eureka, it will use its
+IP Address rather than its hostname.
Circuit Breaker: Hystrix Clients
+Netflix has created a library called Hystrix that implements the circuit breaker pattern. In a microservice architecture it is common to have multiple layers of service calls.
+
+A service failure in the lower level of services can cause cascading failure all the way up to the user. When calls to a particular service reach a certain threshold (20 failures in 5 seconds is the default in Hystrix), the circuit opens and the call is not made. In cases of error and an open circuit a fallback can be provided by the developer.
+
+Having an open circuit stops cascading failures and allows overwhelmed or failing services time to heal. The fallback can be another Hystrix protected call, static data or a sane empty value. Fallbacks may be chained so the first fallback makes some other business call which in turn falls back to static data.
+Example boot app:
+@SpringBootApplication
+@EnableCircuitBreaker
+public class Application {
+
+ public static void main(String[] args) {
+ new SpringApplicationBuilder(Application.class).web(true).run(args);
+ }
+
+}
+
+@Component
+public class StoreIntegration {
+
+ @HystrixCommand(fallbackMethod = "defaultStores")
+ public Object getStores(Map<String, Object> parameters) {
+ //do stuff that might fail
+ }
+
+ public Object defaultStores(Map<String, Object> parameters) {
+ return /* something useful */;
+ }
+}
+The @HystrixCommand is provided by a Netflix contrib library called
+"javanica".
+Spring Cloud automatically wraps Spring beans with that
+annotation in a proxy that is connected to the Hystrix circuit
+breaker. The circuit breaker calculates when to open and close the
+circuit, and what to do in case of a failure.
To configure the @HystrixCommand you can use the commandProperties
+attribute with a list of @HystrixProperty annotations. See
+here
+for more details. See the Hystrix wiki
+for details on the properties available.
Propagating the Security Context or using Spring Scopes
+If you want some thread local context to propagate into a @HystrixCommand the default declaration will not work because it executes the command in a thread pool (in case of timeouts). You can switch Hystrix to use the same thread as the caller using some configuration, or directly in the annotation, by asking it to use a different "Isolation Strategy". For example:
@HystrixCommand(fallbackMethod = "stubMyService",
+ commandProperties = {
+ @HystrixProperty(name="execution.isolation.strategy", value="SEMAPHORE")
+ }
+)
+...The same thing applies if you are using @SessionScope or @RequestScope. You will know when you need to do this because of a runtime exception that says it can’t find the scoped context.
Health Indicator
+The state of the connected circuit breakers are also exposed in the
+/health endpoint of the calling application.
{
+ "hystrix": {
+ "openCircuitBreakers": [
+ "StoreIntegration::getStoresByLocationLink"
+ ],
+ "status": "CIRCUIT_OPEN"
+ },
+ "status": "UP"
+}Hystrix Metrics Stream
+To enable the Hystrix metrics stream include a dependency on spring-boot-starter-actuator. This will expose the /hystrix.stream as a management endpoint.
<dependency>
+ <groupId>org.springframework.boot</groupId>
+ <artifactId>spring-boot-starter-actuator</artifactId>
+ </dependency>Circuit Breaker: Hystrix Dashboard
+One of the main benefits of Hystrix is the set of metrics it gathers about each HystrixCommand. The Hystrix Dashboard displays the health of each circuit breaker in an efficient manner.
+
+To run the Hystrix Dashboard annotate your Spring Boot main class with @EnableHystrixDashboard. You then visit /hystrix and point the dashboard to an individual instances /hystrix.stream endpoint in a Hystrix client application.
Turbine
+Looking at an individual instances Hystrix data is not very useful in terms of the overall health of the system. Turbine is an application that aggregates all of the relevant /hystrix.stream endpoints into a combined /turbine.stream for use in the Hystrix Dashboard. Individual instances are located via Eureka. Running Turbine is as simple as annotating your main class with the @EnableTurbine annotation (e.g. using spring-cloud-starter-turbine to set up the classpath). All of the documented configuration properties from the Turbine 1 wiki apply. The only difference is that the turbine.instanceUrlSuffix does not need the port prepended as this is handled automatically unless turbine.instanceInsertPort=false.
The configuration key turbine.appConfig is a list of eureka serviceIds that turbine will use to lookup instances. The turbine stream is then used in the Hystrix dashboard using a url that looks like: http://my.turbine.sever:8080/turbine.stream?cluster=<CLUSTERNAME>; (the cluster parameter can be omitted if the name is "default"). The cluster parameter must match an entry in turbine.aggregator.clusterConfig. Values returned from eureka are uppercase, thus we expect this example to work if there is an app registered with Eureka called "customers":
turbine: + aggregator: + clusterConfig: CUSTOMERS + appConfig: customers+
The clusterName can be customized by a SPEL expression in turbine.clusterNameExpression with root an instance of InstanceInfo. The default value is appName, which means that the Eureka serviceId ends up as the cluster key (i.e. the InstanceInfo for customers has an appName of "CUSTOMERS"). A different example would be turbine.clusterNameExpression=aSGName, which would get the cluster name from the AWS ASG name. Another example:
turbine: + aggregator: + clusterConfig: SYSTEM,USER + appConfig: customers,stores,ui,admin + clusterNameExpression: metadata['cluster']+
In this case, the cluster name from 4 services is pulled from their metadata map, and is expected to have values that include "SYSTEM" and "USER".
+To use the "default" cluster for all apps you need a string literal expression (with single quotes):
+turbine: + appConfig: customers,stores + clusterNameExpression: 'default'+
Spring Cloud provides a spring-cloud-starter-turbine that has all the dependencies you need to get a Turbine server running. Just create a Spring Boot application and annotate it with @EnableTurbine.
Turbine AMQP
+In some environments (e.g. in a PaaS setting), the classic Turbine model of pulling metrics from all the distributed Hystrix commands doesn’t work. In that case you might want to have your Hystrix commands push metrics to Turbine, and Spring Cloud enables that with AMQP messaging. All you need to do on the client is add a dependency to spring-cloud-netflix-hystrix-amqp and make sure there is a Rabbit broker available (see Spring Boot documentation for details on how to configure the client credentials, but it should work out of the box for a local broker or in Cloud Foundry).
On the server side Just create a Spring Boot application and annotate it with @EnableTurbineAmqp and by default it will come up on port 8989 (point your Hystrix dashboard to that port, any path). You can customize the port using either server.port or turbine.amqp.port. If you have spring-boot-starter-web and spring-boot-starter-actuator on the classpath as well, then you can open up the Actuator endpoints on a separate port (with Tomcat by default) by providing a management.port which is different.
You can then point the Hystrix Dashboard to the Turbine AMQP Server instead of individual Hystrix streams. If Turbine AMQP is running on port 8989 on myhost, then put http://myhost:8989 in the stream input field in the Hystrix Dashboard. Circuits will be prefixed by their respective serviceId, followed by a dot, then the circuit name.
Spring Cloud provides a spring-cloud-starter-turbine-amqp that has all the dependencies you need to get a Turbine AMQP server running. You need Java 8 to run the app because it is Netty-based.
Customizing the AMQP ConnectionFactory
+If you are using AMQP there needs to be a ConnectionFactory (from
+Spring Rabbit) in the application context. If there is a single
+ConnectionFactory it will be used, or if there is a one qualified as
+@HystrixConnectionFactory (on the client) and
+@TurbineConnectionFactory (on the server) it will be preferred over
+others, otherwise the @Primary one will be used. If there are
+multiple unqualified connection factories there will be an error.
Note that Spring Boot (as of 1.2.2) creates a ConnectionFactory that
+is not @Primary, so if you want to use one connection factory for
+the bus and another for business messages, you need to create both,
+and annotate them @*ConnectionFactory and @Primary respectively.
Client Side Load Balancer: Ribbon
+Ribbon is a client side load balancer which gives you a lot of control
+over the behaviour of HTTP and TCP clients. Feign already uses Ribbon,
+so if you are using @FeignClient then this section also applies.
A central concept in Ribbon is that of the named client. Each load
+balancer is part of an ensemble of components that work together to
+contact a remote server on demand, and the ensemble has a name that
+you give it as an application developer (e.g. using the @FeignClient
+annotation). Spring Cloud creates a new ensemble as an
+ApplicationContext on demand for each named client using
+RibbonClientConfiguration. This contains (amongst other things) an
+ILoadBalancer, a RestClient, and a ServerListFilter.
Customizing the Ribbon Client
+You can configure some bits of a Ribbon client using external
+properties in <client>.ribbon.*, which is no different than using
+the Netflix APIs natively, except that you can use Spring Boot
+configuration files. The native options can
+be inspected as static fields in CommonClientConfigKey (part of
+ribbon-core).
Spring Cloud also lets you take full control of the client by
+declaring additional configuration (on top of the
+RibbonClientConfiguration) using @RibbonClient. Example:
@Configuration
+@RibbonClient(name = "foo", configuration = FooConfiguration.class)
+public class TestConfiguration {
+}In this case the client is composed from the components already in
+RibbonClientConfiguration together with any in FooConfiguration
+(where the latter generally will override the former).
|
+ Warning
+ |
+
+The FooConfiguration has to be @Configuration but take
+care that it is not in a @ComponentScan for the main application
+context, otherwise it will be shared by all the @RibbonClients. If
+you use @ComponentScan (or @SpringBootApplication) you need to
+take steps to avoid it being included (for instance put it in a
+separate, non-overlapping package, or specify the packages to scan
+explicitly in the @ComponentScan).
+ |
+
Spring Cloud Netflix provides the following beans by default for ribbon
+(BeanType beanName: ClassName):
-
+
-
+
+IClientConfigribbonClientConfig:DefaultClientConfigImpl
+ -
+
+IRuleribbonRule:ZoneAvoidanceRule
+ -
+
+IPingribbonPing:NoOpPing
+ -
+
+ServerList<Server>ribbonServerList:ConfigurationBasedServerList
+ -
+
+ServerListFilter<Server>ribbonServerListFilter:ZonePreferenceServerListFilter
+ -
+
+ILoadBalancerribbonLoadBalancer:ZoneAwareLoadBalancer
+
Creating a bean of one of those type and placing it in a @RibbonClient
+configuration (such as FooConfiguration above) allows you to override each
+one of the beans described. Example:
@Configuration
+public class FooConfiguration {
+ @Bean
+ public IPing ribbonPing(IClientConfig config) {
+ return new PingUrl();
+ }
+}This replaces the NoOpPing with PingUrl.
Using Ribbon with Eureka
+When Eureka is used in conjunction with Ribbon the ribbonServerList
+is overridden with an extension of DiscoveryEnabledNIWSServerList
+which populates the list of servers from Eureka. It also replaces the
+IPing interface with NIWSDiscoveryPing which delegates to Eureka
+to determine if a server is up. The ServerList that is installed by
+default is a DomainExtractingServerList and the purpose of this is
+to make physical metadata available to the load balancer without using
+AWS AMI metadata (which is what Netflix relies on). By default the
+server list will be constructed with "zone" information as provided in
+the instance metadata (so on the client set
+eureka.instance.metadataMap.zone), and if that is missing it can use
+the domain name from the server hostname as a proxy for zone (if the
+flag approximateZoneFromHostname is set). Once the zone information is
+available it can be used in a ServerListFilter (by default it will
+be used to locate a server in the same zone as the client because the
+default is a ZonePreferenceServerListFilter).
Example: How to Use Ribbon Without Eureka
+Eureka is a convenient way to abstract the discovery of remote servers
+so you don’t have to hard code their URLs in clients, but if you
+prefer not to use it, Ribbon and Feign are still quite
+amenable. Suppose you have declared a @RibbonClient for "stores",
+and Eureka is not in use (and not even on the classpath). The Ribbon
+client defaults to a configured server list, and you can supply the
+configuration like this
stores: + ribbon: + listOfServers: example.com,google.com+
Example: Disable Eureka use in Ribbon
+Setting the property ribbon.eureka.enabled = false will explicitly
+disable the use of Eureka in Ribbon.
ribbon: + eureka: + enabled: false+
Using the Ribbon API Directly
+You can also use the LoadBalancerClient directly. Example:
public class MyClass {
+ @Autowired
+ private LoadBalancerClient loadBalancer;
+
+ public void doStuff() {
+ ServiceInstance instance = loadBalancer.choose("stores");
+ URI storesUri = URI.create(String.format("http://%s:%s", instance.getHost(), instance.getPort()));
+ // ... do something with the URI
+ }
+}Declarative REST Client: Feign
+Feign is a declarative web service client. It makes writing web service clients easier. To use Feign create an interface and annotate it. It has pluggable annotation support including Feign annotations and JAX-RS annotations. Feign also supports pluggable encoders and decoders. Spring Cloud adds support for Spring MVC annotations and for using the same HttpMessageConverters used by default in Spring Web. Spring Cloud integrates Ribbon and Eureka to provide a load balanced http client when using Feign.
Example spring boot app
+@Configuration
+@ComponentScan
+@EnableAutoConfiguration
+@EnableEurekaClient
+@EnableFeignClients
+public class Application {
+
+ public static void main(String[] args) {
+ SpringApplication.run(Application.class, args);
+ }
+
+}@FeignClient("stores")
+public interface StoreClient {
+ @RequestMapping(method = RequestMethod.GET, value = "/stores")
+ List<Store> getStores();
+
+ @RequestMapping(method = RequestMethod.POST, value = "/stores/{storeId}", consumes = "application/json")
+ Store update(@PathVariable("storeId") Long storeId, Store store);
+}In the @FeignClient annotation the String value ("stores" above) is
+an arbitrary client name, which is used to create a Ribbon load
+balancer (see below for details of Ribbon
+support). You can also specify a URL using the url attribute
+(absolute value or just a hostname).
The Ribbon client above will want to discover the physical addresses +for the "stores" service. If your application is a Eureka client then +it will resolve the service in the Eureka service registry. If you +don’t want to use Eureka, you can simply configure a list of servers +in your external configuration (see +above for example).
+Overriding Feign Defaults
+A central concept in Spring Cloud’s Feign support is that of the named client. Each feign client is part of an ensemble of components that work together to contact a remote server on demand, and the ensemble has a name that you give it as an application developer using the @FeignClient annotation. Spring Cloud creates a new ensemble as an
+ApplicationContext on demand for each named client using FeignClientsConfiguration. This contains (amongst other things) an feign.Decoder, a feign.Encoder, and a feign.Contract.
Spring Cloud lets you take full control of the feign client by declaring additional configuration (on top of the FeignClientsConfiguration) using @FeignClient. Example:
@FeignClient(name = "stores", configuration = FooConfiguration.class)
+public interface StoreClient {
+ //..
+}In this case the client is composed from the components already in FeignClientsConfiguration together with any in FooConfiguration (where the latter will override the former).
|
+ Warning
+ |
+
+The FooConfiguration has to be @Configuration but take care that it is not in a @ComponentScan for the main application context, otherwise it will be used for every @FeignClient. If you use @ComponentScan (or @SpringBootApplication) you need to take steps to avoid it being included (for instance put it in a separate, non-overlapping package, or specify the packages to scan explicitly in the @ComponentScan).
+ |
+
|
+ Note
+ |
+
+The serviceId attribute is now deprecated in favor of the name attribute.
+ |
+
|
+ Warning
+ |
+
+Previously, using the url attribute, did not require the name attribute. Using name is now required.
+ |
+
Placeholders are supported in the name and url attributes.
@FeignClient(name = "${feign.name}", url = "${feign.url}")
+public interface StoreClient {
+ //..
+}Spring Cloud Netflix provides the following beans by default for feign (BeanType beanName: ClassName):
-
+
-
+
+DecoderfeignDecoder:ResponseEntityDecoder(which wraps aSpringDecoder)
+ -
+
+EncoderfeignEncoder:SpringEncoder
+ -
+
+LoggerfeignLogger:Slf4jLogger
+ -
+
+ContractfeignContract:SpringMvcContract
+ -
+
+Feign.BuilderfeignBuilder:HystrixFeign.Builder
+
Spring Cloud Netflix does not provide the following beans by default for feign, but still looks up beans of these types from the application context to create the feign client:
+-
+
-
+
+Logger.Level
+ -
+
+Retryer
+ -
+
+ErrorDecoder
+ -
+
+Request.Options
+ -
+
+Collection<RequestInterceptor>
+
Creating a bean of one of those type and placing it in a @FeignClient configuration (such as FooConfiguration above) allows you to override each one of the beans described. Example:
@Configuration
+public class FooConfiguration {
+ @Bean
+ public Contract feignContractg() {
+ return new feign.Contract.Default();
+ }
+
+ @Bean
+ public BasicAuthRequestInterceptor basicAuthRequestInterceptor() {
+ return new BasicAuthRequestInterceptor("user", "password");
+ }
+}This replaces the SpringMvcContract with feign.Contract.Default and adds a RequestInterceptor to the collection of RequestInterceptor.
Default configurations can be specified in the @EnableFeignClients attribute defaultConfiguration in a similar manner as described above. The difference is that this configuration will apply to all feign clients.
Feign Hystrix Support
+If Hystrix is on the classpath, by default Feign will wrap all methods with a circuit breaker. Returning a com.netflix.hystrix.HystrixCommand is also available. This lets you use reactive patterns (with a call to .toObservable() or .observe() or asynchronous use (with a call to .queue()).
To disable Hystrix support for Feign, set feign.hystrix.enabled=false.
To disable Hystrix support on a per-client basis create a vanilla Feign.Builder with the "prototype" scope, e.g.:
@Configuration
+public class FooConfiguration {
+ @Bean
+ @Scope("prototype")
+ public Feign.Builder feignBuilder() {
+ return Feign.builder();
+ }
+}Feign Hystrix Fallbacks
+Hystrix supports the notion of a fallback: a default code path that is executed when they circuit is open or there is an error. To enable fallbacks for a given @FeignClient set the fallback attribute to the class name that implements the fallback.
@FeignClient(name = "hello", fallback = HystrixClientFallback.class)
+protected interface HystrixClient {
+ @RequestMapping(method = RequestMethod.GET, value = "/hello")
+ Hello iFailSometimes();
+}
+
+static class HystrixClientFallback implements HystrixClient {
+ @Override
+ public Hello iFailSometimes() {
+ return new Hello("fallback");
+ }
+}|
+ Warning
+ |
+
+There is a limitation with the implementation of fallbacks in Feign and how Hystrix fallbacks work. Fallbacks are currently not supported for methods that return com.netflix.hystrix.HystrixCommand and rx.Observable.
+ |
+
Feign Inheritance Support
+Feign supports boilerplate apis via single-inheritance interfaces. +This allows grouping common operations into convenient base interfaces. +Together with Spring MVC you can share the same contract for your +REST endpoint and Feign client.
+public interface UserService {
+
+ @RequestMapping(method = RequestMethod.GET, value ="/users/{id}")
+ User getUser(@PathVariable("id") long id);
+}@RestController
+public class UserResource implements UserService {
+
+}package project.user;
+
+@FeignClient("users")
+public interface UserClient extends UserService {
+
+}Feign request/response compression
+You may consider enabling the request or response GZIP compression for your +Feign requests. You can do this by enabling one of the properties:
+feign.compression.request.enabled=true
+feign.compression.response.enabled=trueFeign request compression gives you settings similar to what you may set for your web server:
+feign.compression.request.enabled=true
+feign.compression.request.mime-types=text/xml,application/xml,application/json
+feign.compression.request.min-request-size=2048These properties allow you to be selective about the compressed media types and minimum request threshold length.
+Feign logging
+A logger is created for each Feign client created. By default the name of the logger is the full class name of the interface used to create the Feign client. Feign logging only responds to the DEBUG level.
logging.level.project.user.UserClient: DEBUGThe Logger.Level object that you may configure per client, tells Feign how much to log. Choices are:
-
+
-
+
+NONE, No logging (DEFAULT).
+ -
+
+BASIC, Log only the request method and URL and the response status code and execution time.
+ -
+
+HEADERS, Log the basic information along with request and response headers.
+ -
+
+FULL, Log the headers, body, and metadata for both requests and responses.
+
For example, the following would set the Logger.Level to FULL:
@Configuration
+public class FooConfiguration {
+ @Bean
+ Logger.Level feignLoggerLevel() {
+ return Logger.Level.FULL;
+ }
+}External Configuration: Archaius
+Archaius is the Netflix client side configuration library. It is the library used by all of the Netflix OSS components for configuration. Archaius is an extension of the Apache Commons Configuration project. It allows updates to configuration by either polling a source for changes or for a source to push changes to the client. Archaius uses Dynamic<Type>Property classes as handles to properties.
+class ArchaiusTest {
+ DynamicStringProperty myprop = DynamicPropertyFactory
+ .getInstance()
+ .getStringProperty("my.prop");
+
+ void doSomething() {
+ OtherClass.someMethod(myprop.get());
+ }
+}Archaius has its own set of configuration files and loading priorities. Spring applications should generally not use Archaius directly, but the need to configure the Netflix tools natively remains. Spring Cloud has a Spring Environment Bridge so Archaius can read properties from the Spring Environment. This allows Spring Boot projects to use the normal configuration toolchain, while allowing them to configure the Netflix tools, for the most part, as documented.
+Router and Filter: Zuul
+Routing in an integral part of a microservice architecture. For example, / may be mapped to your web application, /api/users is mapped to the user service and /api/shop is mapped to the shop service. Zuul is a JVM based router and server side load balancer by Netflix.
Netflix uses Zuul for the following:
+-
+
-
+
Authentication
+
+ -
+
Insights
+
+ -
+
Stress Testing
+
+ -
+
Canary Testing
+
+ -
+
Dynamic Routing
+
+ -
+
Service Migration
+
+ -
+
Load Shedding
+
+ -
+
Security
+
+ -
+
Static Response handling
+
+ -
+
Active/Active traffic management
+
+
Zuul’s rule engine allows rules and filters to be written in essentially any JVM language, with built in support for Java and Groovy.
+Embedded Zuul Reverse Proxy
+Spring Cloud has created an embedded Zuul proxy to ease the +development of a very common use case where a UI application wants to +proxy calls to one or more back end services. This feature is useful +for a user interface to proxy to the backend services it requires, +avoiding the need to manage CORS and authentication concerns +independently for all the backends.
+To enable it, annotate a Spring Boot main class with
+@EnableZuulProxy, and this forwards local calls to the appropriate
+service. By convention, a service with the Eureka ID "users", will
+receive requests from the proxy located at /users (with the prefix
+stripped). The proxy uses Ribbon to locate an instance to forward to
+via Eureka, and all requests are executed in a hystrix command, so
+failures will show up in Hystrix metrics, and once the circuit is open
+the proxy will not try to contact the service.
To skip having a service automatically added, set
+zuul.ignored-services to a list of service id patterns. If a service
+matches a pattern that is ignored, but also included in the explicitly
+configured routes map, then it will be unignored. Example:
zuul:
+ ignoredServices: '*'
+ routes:
+ users: /myusers/**In this example, all services are ignored except "users".
+To augment or change +the proxy routes, you can add external configuration like the +following:
+ zuul:
+ routes:
+ users: /myusers/**This means that http calls to "/myusers" get forwarded to the "users" +service (for example "/myusers/101" is forwarded to "/101").
+To get more fine-grained control over a route you can specify the path +and the serviceId independently:
+ zuul:
+ routes:
+ users:
+ path: /myusers/**
+ serviceId: users_serviceThis means that http calls to "/myusers" get forwarded to the +"users_service" service. The route has to have a "path" which can be +specified as an ant-style pattern, so "/myusers/*" only matches one +level, but "/myusers/**" matches hierarchically.
+The location of the backend can be specified as either a "serviceId" +(for a Eureka service) or a "url" (for a physical location), e.g.
+ zuul:
+ routes:
+ users:
+ path: /myusers/**
+ url: http://example.com/users_serviceThese simple url-routes doesn’t get executed as HystrixCommand nor can you loadbalance multiple url with Ribbon. +To achieve this specify a service-route and configure a Ribbon client for the +serviceId (this currently requires disabling Eureka support in Ribbon: +see above for more information), e.g.
+zuul:
+ routes:
+ users:
+ path: /myusers/**
+ serviceId: users
+
+ribbon:
+ eureka:
+ enabled: false
+
+users:
+ ribbon:
+ listOfServers: example.com,google.comYou can provide convention between serviceId and routes using +regexmapper. It uses regular expression named group to extract +variables from serviceId and inject them into a route pattern.
+@Bean
+public PatternServiceRouteMapper serviceRouteMapper() {
+ return new PatternServiceRouteMapper(
+ "(?<name>^.+)-(?<version>v.+$)",
+ "${version}/${name}");
+}This means that a serviceId "myusers-v1" will be mapped to route +"/v1/myusers/**". Any regular expression is accepted but all named +group must be present in both servicePattern and routePattern. If +servicePattern do not match a serviceId, the default behavior is +used. In exemple above, a serviceId "myusers" will be mapped to route +"/myusers/**" (no version detected) These feature is disable by +default and is only applied to discovered services.
+To add a prefix to all mappings, set zuul.prefix to a value, such as
+/api. The proxy prefix is stripped from the request before the
+request is forwarded by default (switch this behaviour off with
+zuul.stripPrefix=false). You can also switch off the stripping of
+the service-specific prefix from individual routes, e.g.
zuul:
+ routes:
+ users:
+ path: /myusers/**
+ stripPrefix: falseIn this example requests to "/myusers/101" will be forwarded to "/myusers/101" on the "users" service.
+The zuul.routes entries actually bind to an object of type ProxyRouteLocator. If you
+look at the properties of that object you will see that it also has a "retryable" flag.
+Set that flag to "true" to have the Ribbon client automatically retry failed requests
+(and if you need to you can modify the parameters of the retry operations using
+the Ribbon client configuration).
The X-Forwarded-Host header is added to the forwarded requests by
+default. To turn it off set zuul.addProxyHeaders = false. The
+prefix path is stripped by default, and the request to the backend
+picks up a header "X-Forwarded-Prefix" ("/myusers" in the examples
+above).
An application with the @EnableZuulProxy could act as a standalone
+server if you set a default route ("/"), for example zuul.route.home:
+/ would route all traffic (i.e. "/**") to the "home" service.
If more fine-grained ignoring is needed, you can specify specific patterns to ignore. +These patterns are being evaluated at the start of the route location process, which +means prefixes should be included in the pattern to warrant a match. Ignored patterns +span all services and supersede any other route specification.
+ zuul:
+ ignoredPatterns: /**/admin/**
+ routes:
+ users: /myusers/**This means that all calls such as "/myusers/101" will be forwarded to "/101" on the "users" service. +But calls including "/admin/" will not resolve.
+Strangulation Patterns and Local Forwards
+A common pattern when migrating an existing application or API is to +"strangle" old endpoints, slowly replacing them with different +implementations. The Zuul proxy is a useful tool for this because you +can use it to handle all traffic from clients of the old endpoints, +but redirect some of the requests to new ones.
+Example configuration:
+ zuul:
+ routes:
+ first:
+ path: /first/**
+ url: http://first.example.com
+ second:
+ path: /second/**
+ url: forward:/second
+ third:
+ path: /third/**
+ url: forward:/3rd
+ legacy:
+ path: /**
+ url: http://legacy.example.comIn this example we are strangling the "legacy" app which is mapped to
+all requests that do not match one of the other patterns. Paths in
+/first/** have been extracted into a new service with an external
+URL. And paths in /second/** are forwared so they can be handled
+locally, e.g. with a normal Spring @RequestMapping. Paths in
+/third/** are also forwarded, but with a different prefix
+(i.e. /third/foo is forwarded to /3rd/foo).
|
+ Note
+ |
++The ignored pattterns aren’t completely ignored, they just +aren’t handled by the proxy (so they are also effectively forwarded +locally). + | +
Uploading Files through Zuul
+If you @EnableZuulProxy you can use the proxy paths to
+upload files and it should just work as long as the files
+are small. For large files there is an alternative path
+which bypasses the Spring DispatcherServlet (to
+avoid multipart processing) in "/zuul/*". I.e. if
+zuul.routes.customers=/customers/** then you can
+POST large files to "/zuul/customers/*". The servlet
+path is externalized via zuul.servletPath. Extremely
+large files will also require elevated timeout settings
+if the proxy route takes you through a Ribbon load
+balancer, e.g.
hystrix.command.default.execution.isolation.thread.timeoutInMilliseconds: 60000
+ribbon:
+ ConnectTimeout: 3000
+ ReadTimeout: 60000Note that for streaming to work with large files, you need to use chunked encoding in the request (which some browsers +do not do by default). E.g. on the command line:
+$ curl -v -H "Transfer-Encoding: chunked" \ + -F "file=@mylarge.iso" localhost:9999/zuul/simple/file+
Plain Embedded Zuul
+You can also run a Zuul server without the proxying, or switch on parts of the proxying platform selectively, if you
+use @EnableZuulServer (instead of @EnableZuulProxy). Any beans that you add to the application of type ZuulFilter
+will be installed automatically, as they are with @EnableZuulProxy, but without any of the proxy filters being added
+automatically.
In this case the routes into the Zuul server are still specified by +configuring "zuul.routes.*", but there is no service +discovery and no proxying, so the "serviceId" and "url" settings are +ignored. For example:
+ zuul:
+ routes:
+ api: /api/**maps all paths in "/api/**" to the Zuul filter chain.
+Disable Zuul Filters
+Zuul for Spring Cloud comes with a number of ZuulFilter beans enabled by default
+in both proxy and server mode. See the zuul filters package for the
+possible filters that are enabled. If you want to disable one, simply set
+zuul.<SimpleClassName>.<filterType>.disable=true. By convention, the package after
+filters is the Zuul filter type. For example to disable
+org.springframework.cloud.netflix.zuul.filters.post.SendResponseFilter set
+zuul.SendResponseFilter.post.disable=true.
Polyglot support with Sidecar
+Do you have non-jvm languages you want to take advantage of Eureka, Ribbon and +Config Server? The Spring Cloud Netflix Sidecar was inspired by +Netflix Prana. It includes a simple http api +to get all of the instances (ie host and port) for a given service. You can +also proxy service calls through an embedded Zuul proxy which gets its route +entries from Eureka. The Spring Cloud Config Server can be accessed directly +via host lookup or through the Zuul Proxy. The non-jvm app should implement +a health check so the Sidecar can report to eureka if the app is up or down.
+To enable the Sidecar, create a Spring Boot application with @EnableSidecar.
+This annotation includes @EnableCircuitBreaker, @EnableDiscoveryClient,
+and @EnableZuulProxy. Run the resulting application on the same host as the
+non-jvm application.
To configure the side car add sidecar.port and sidecar.health-uri to application.yml.
+The sidecar.port property is the port the non-jvm app is listening on. This
+is so the Sidecar can properly register the app with Eureka. The sidecar.health-uri
+is a uri accessible on the non-jvm app that mimicks a Spring Boot health
+indicator. It should return a json document like the following:
{
+ "status":"UP"
+}Here is an example application.yml for a Sidecar application:
+server:
+ port: 5678
+spring:
+ application:
+ name: sidecar
+
+sidecar:
+ port: 8000
+ health-uri: http://localhost:8000/health.jsonThe api for the DiscoveryClient.getInstances() method is /hosts/{serviceId}.
+Here is an example response for /hosts/customers that returns two instances on
+different hosts. This api is accessible to the non-jvm app (if the sidecar is
+on port 5678) at http://localhost:5678/hosts/{serviceId}.
[
+ {
+ "host": "myhost",
+ "port": 9000,
+ "uri": "http://myhost:9000",
+ "serviceId": "CUSTOMERS",
+ "secure": false
+ },
+ {
+ "host": "myhost2",
+ "port": 9000,
+ "uri": "http://myhost2:9000",
+ "serviceId": "CUSTOMERS",
+ "secure": false
+ }
+]The Zuul proxy automatically adds routes for each service known in eureka to
+/<serviceId>, so the customers service is available at /customers. The
+Non-jvm app can access the customer service via http://localhost:5678/customers
+(assuming the sidecar is listening on port 5678).
If the Config Server is registered with Eureka, non-jvm application can access
+it via the Zuul proxy. If the serviceId of the ConfigServer is configserver
+and the Sidecar is on port 5678, then it can be accessed at
+http://localhost:5678/configserver
Non-jvm app can take advantage of the Config Server’s ability to return YAML +documents. For example, a call to http://sidecar.local.spring.io:5678/configserver/default-master.yml +might result in a YAML document like the following
+eureka:
+ client:
+ serviceUrl:
+ defaultZone: http://localhost:8761/eureka/
+ password: password
+info:
+ description: Spring Cloud Samples
+ url: https://github.com/spring-cloud-samplesMetrics: Spectator, Servo, and Atlas
+When used together, Spectator/Servo and Atlas provide a near real-time operational insight platform.
+Spectator and Servo are Netflix’s metrics collection libraries. Atlas is a Netflix metrics backend to manage dimensional time series data.
+Servo served Netflix for several years and is still usable, but is gradually being phased out in favor of Spectator, which is only designed to work with Java 8. Spring Cloud Netflix provides support for both, but Java 8 based applications are encouraged to use Spectator.
+Dimensional vs. Hierarchical Metrics
+Spring Boot Actuator metrics are hierarchical and metrics are separated only by name. These names often follow a naming convention that embeds key/value attribute pairs (dimensions) into the name separated by periods. Consider the following metrics for two endpoints, root and star-star:
+{
+ "counter.status.200.root": 20,
+ "counter.status.400.root": 3,
+ "counter.status.200.star-star": 5,
+}The first metric gives us a normalized count of successful requests against the root endpoint per unit of time. But what if the system had 20 endpoints and you want to get a count of successful requests against all the endpoints? Some hierarchical metrics backends would allow you to specify a wild card such as counter.status.200. that would read all 20 metrics and aggregate the results. Alternatively, you could provide a HandlerInterceptorAdapter that intercepts and records a metric like counter.status.200.all for all successful requests irrespective of the endpoint, but now you must write 20+1 different metrics. Similarly if you want to know the total number of successful requests for all endpoints in the service, you could specify a wild card such as counter.status.2.*.
Even in the presence of wildcarding support on a hierarchical metrics backend, naming consistency can be difficult. Specifically the position of these tags in the name string can slip with time, breaking queries. For example, suppose we add an additional dimension to the hierarchical metrics above for HTTP method. Then counter.status.200.root becomes counter.status.200.method.get.root, etc. Our counter.status.200.* suddenly no longer has the same semantic meaning. Furthermore, if the new dimension is not applied uniformly across the codebase, certain queries may become impossible. This can quickly get out of hand.
Netflix metrics are tagged (a.k.a. dimensional). Each metric has a name, but this single named metric can contain multiple statistics and 'tag' key/value pairs that allows more querying flexibility. In fact, the statistics themselves are recorded in a special tag.
+Recorded with Netflix Servo or Spectator, a timer for the root endpoint described above contains 4 statistics per status code, where the count statistic is identical to Spring Boot Actuator’s counter. In the event that we have encountered an HTTP 200 and 400 thus far, there will be 8 available data points:
+{
+ "root(status=200,stastic=count)": 20,
+ "root(status=200,stastic=max)": 0.7265630630000001,
+ "root(status=200,stastic=totalOfSquares)": 0.04759702862580789,
+ "root(status=200,stastic=totalTime)": 0.2093076914666667,
+ "root(status=400,stastic=count)": 1,
+ "root(status=400,stastic=max)": 0,
+ "root(status=400,stastic=totalOfSquares)": 0,
+ "root(status=400,stastic=totalTime)": 0,
+}Default Metrics Collection
+Without any additional dependencies or configuration, a Spring Cloud based service will autoconfigure a Servo MonitorRegistry and begin collecting metrics on every Spring MVC request. By default, a Servo timer with the name rest will be recorded for each MVC request which is tagged with:
-
+
-
+
HTTP method
+
+ -
+
HTTP status (e.g. 200, 400, 500)
+
+ -
+
URI (or "root" if the URI is empty), sanitized for Atlas
+
+ -
+
The exception class name, if the request handler threw an exception
+
+ -
+
The caller, if a request header with a key matching
+netflix.metrics.rest.callerHeaderis set on the request. There is no default key fornetflix.metrics.rest.callerHeader. You must add it to your application properties if you wish to collect caller information.
+
Set the netflix.metrics.rest.metricName property to change the name of the metric from rest to a name you provide.
If Spring AOP is enabled and org.aspectj:aspectjweaver is present on your runtime classpath, Spring Cloud will also collect metrics on every client call made with RestTemplate. A Servo timer with the name of restclient will be recorded for each MVC request which is tagged with:
-
+
-
+
HTTP method
+
+ -
+
HTTP status (e.g. 200, 400, 500), "CLIENT_ERROR" if the response returned null, or "IO_ERROR" if an
+IOExceptionoccurred during the execution of theRestTemplatemethod
+ -
+
URI, sanitized for Atlas
+
+ -
+
Client name
+
+
Metrics Collection: Spectator
+To enable Spectator metrics, include a dependency on spring-boot-starter-spectator:
<dependency>
+ <groupId>org.springframework.cloud</groupId>
+ <artifactId>spring-cloud-starter-spectator</artifactId>
+ </dependency>In Spectator parlance, a meter is a named, typed, and tagged configuration and a metric represents the value of a given meter at a point in time. Spectator meters are created and controlled by a registry, which currently has several different implementations. Spectator provides 4 meter types: counter, timer, gauge, and distribution summary.
+Spring Cloud Spectator integration configures an injectable com.netflix.spectator.api.Registry instance for you. Specifically, it configures a ServoRegistry instance in order to unify the collection of REST metrics and the exporting of metrics to the Atlas backend under a single Servo API. Practically, this means that your code may use a mixture of Servo monitors and Spectator meters and both will be scooped up by Spring Boot Actuator MetricReader instances and both will be shipped to the Atlas backend.
Spectator Counter
+A counter is used to measure the rate at which some event is occurring.
+// create a counter with a name and a set of tags
+Counter counter = registry.counter("counterName", "tagKey1", "tagValue1", ...);
+counter.increment(); // increment when an event occurs
+counter.increment(10); // increment by a discrete amountThe counter records a single time-normalized statistic.
+Spectator Timer
+A timer is used to measure how long some event is taking. Spring Cloud automatically records timers for Spring MVC requests and conditionally RestTemplate requests, which can later be used to create dashboards for request related metrics like latency:
image::RequestLatency.png []
+// create a timer with a name and a set of tags
+Timer timer = registry.timer("timerName", "tagKey1", "tagValue1", ...);
+
+// execute an operation and time it at the same time
+T result = timer.record(() -> fooReturnsT());
+
+// alternatively, if you must manually record the time
+Long start = System.nanoTime();
+T result = fooReturnsT();
+timer.record(System.nanoTime() - start, TimeUnit.NANOSECONDS);The timer simultaneously records 4 statistics: count, max, totalOfSquares, and totalTime. The count statistic will always match the single normalized value provided by a counter if you had called increment() once on the counter for each time you recorded a timing, so it is rarely necessary to count and time separately for a single operation.
For long running operations, Spectator provides a special LongTaskTimer.
Spectator Gauge
+Gauges are used to determine some current value like the size of a queue or number of threads in a running state. Since gauges are sampled, they provide no information about how these values fluctuate between samples.
+The normal use of a gauge involves registering the gauge once in initialization with an id, a reference to the object to be sampled, and a function to get or compute a numeric value based on the object. The reference to the object is passed in separately and the Spectator registry will keep a weak reference to the object. If the object is garbage collected, then Spectator will automatically drop the registration. See the note in Spectator’s documentation about potential memory leaks if this API is misused.
+// the registry will automatically sample this gauge periodically
+registry.gauge("gaugeName", pool, Pool::numberOfRunningThreads);
+
+// manually sample a value in code at periodic intervals -- last resort!
+registry.gauge("gaugeName", Arrays.asList("tagKey1", "tagValue1", ...), 1000);Spectator Distribution Summaries
+A distribution summary is used to track the distribution of events. It is similar to a timer, but more general in that the size does not have to be a period of time. For example, a distribution summary could be used to measure the payload sizes of requests hitting a server.
+// the registry will automatically sample this gauge periodically
+DistributionSummary ds = registry.distributionSummary("dsName", "tagKey1", "tagValue1", ...);
+ds.record(request.sizeInBytes());Metrics Collection: Servo
+|
+ Warning
+ |
++If your code is compiled on Java 8, please use Spectator instead of Servo as Spectator is destined to replace Servo entirely in the long term. + | +
In Servo parlance, a monitor is a named, typed, and tagged configuration and a metric represents the value of a given monitor at a point in time. Servo monitors are logically equivalent to Spectator meters. Servo monitors are created and controlled by a MonitorRegistry. In spite of the above warning, Servo does have a wider array of monitor options than Spectator has meters.
Spring Cloud integration configures an injectable com.netflix.servo.MonitorRegistry instance for you. Once you have created the appropriate Monitor type in Servo, the process of recording data is wholly similar to Spectator.
Creating Servo Monitors
+If you are using the Servo MonitorRegistry instance provided by Spring Cloud (specifically, an instance of DefaultMonitorRegistry), Servo provides convenience classes for retrieving counters and timers. These convenience classes ensure that only one Monitor is registered for each unique combination of name and tags.
To manually create a Monitor type in Servo, especially for the more exotic monitor types for which convenience methods are not provided, instantiate the appropriate type by providing a MonitorConfig instance:
MonitorConfig config = MonitorConfig.builder("timerName").withTag("tagKey1", "tagValue1").build();
+
+// somewhere we should cache this Monitor by MonitorConfig
+Timer timer = new BasicTimer(config);
+monitorRegistry.register(timer);Metrics Backend: Atlas
+Atlas was developed by Netflix to manage dimensional time series data for near real-time operational insight. Atlas features in-memory data storage, allowing it to gather and report very large numbers of metrics, very quickly.
+Atlas captures operational intelligence. Whereas business intelligence is data gathered for analyzing trends over time, operational intelligence provides a picture of what is currently happening within a system.
+Spring Cloud provides a spring-cloud-starter-atlas that has all the dependencies you need. Then just annotate your Spring Boot application with @EnableAtlas and provide a location for your running Atlas server with the netflix.atlas.uri property.
Global tags
+Spring Cloud enables you to add tags to every metric sent to the Atlas backend. Global tags can be used to separate metrics by application name, environment, region, etc.
+Each bean implementing AtlasTagProvider will contribute to the global tag list:
@Bean
+AtlasTagProvider atlasCommonTags(
+ @Value("${spring.application.name}") String appName) {
+ return () -> Collections.singletonMap("app", appName);
+}Using Atlas
+To bootstrap a in-memory standalone Atlas instance:
+$ curl -LO https://github.com/Netflix/atlas/releases/download/v1.4.2/atlas-1.4.2-standalone.jar
+$ java -jar atlas-1.4.2-standalone.jar|
+ Tip
+ |
++An Atlas standalone node running on an r3.2xlarge (61GB RAM) can handle roughly 2 million metrics per minute for a given 6 hour window. + | +
Once running and you have collected a handful of metrics, verify that your setup is correct by listing tags on the Atlas server:
+$ curl http://ATLAS/api/v1/tags|
+ Tip
+ |
+
+After executing several requests against your service, you can gather some very basic information on the request latency of every request by pasting the following url in your browser: http://ATLAS/api/v1/graph?q=name,rest,:eq,:avg
+ |
+
The Atlas wiki contains a compilation of sample queries for various scenarios.
+Make sure to check out the alerting philosophy and docs on using double exponential smoothing to generate dynamic alert thresholds.
+Spring Cloud Bus
+Spring Cloud Bus links nodes of a distributed system with a lightweight message broker. This can then be used to broadcast state changes (e.g. configuration changes) or other management instructions. A key idea is that the Bus is like a distributed Actuator for a Spring Boot application that is scaled out, but it can also be used as a communication channel between apps. The only implementation currently is with an AMQP broker as the transport, but the same basic feature set (and some more depending on the transport) is on the roadmap for other transports.
+Quick Start
+Spring Cloud Bus works by adding Spring Boot autconfiguration if it detects itself on the classpath. All you need to do to enable the bus is to add spring-cloud-starter-bus-amqp to your dependency management and Spring Cloud takes care of the rest. Make sure RabbitMQ is available and configured to provide a ConnectionFactory: running on localhost you shouldn’t have to do anything, but if you are running remotely use Spring Cloud Connectors, or Spring Boot conventions to define the broker credentials, e.g.
spring: + rabbitmq: + host: mybroker.com + port: 5672 + username: user + password: secret+
The bus currently supports sending messages to all nodes listening or all nodes for a particular service (as defined by Eureka). More selector criteria will be added in the future (ie. only service X nodes in data center Y, etc…). The http endpoints are under the /bus/* actuator namespace. There are currently two implemented. The first, /bus/env, sends key/values pairs to update each nodes Spring Environment. The second, /bus/refresh, will reload each application’s configuration, just as if they had all been pinged on their /refresh endpoint.
Addressing an Instance
+The HTTP endpoints accept a "destination" parameter, e.g. "/bus/refresh?destination=customers:9000", where the destination is an ApplicationContext ID. If the ID is owned by an instance on the Bus then it will process the message and all other instances will ignore it. Spring Boot sets the ID for you in the ContextIdApplicationContextInitializer to a combination of the spring.application.name, active profiles and server.port by default.
Addressing all instances of a service
+The "destination" parameter is used in a Spring PathMatcher (with the path separator as a colon :) to determine if an instance will process the message. Using the example from above, "/bus/refresh?destination=customers:**" will target all instances of the "customers" service regardless of the profiles and ports set as the ApplicationContext ID.
Application Context ID must be unique
+The bus tries to eliminate processing an event twice, once from the original ApplicationEvent and once from the queue. To do this, it checks the sending application context id againts the current application context id. If multiple instances of a service have the same application context id, events will not be processed. Running on a local machine, each service will be on a different port and that will be part of the application context id. Cloud Foundry supplies an index to differentiate. To ensure that the application context id is the unique, set spring.application.index to something unique for each instance of a service. For example, in lattice, set spring.application.index=${INSTANCE_INDEX} in application.properties (or bootstrap.properties if using configserver).
Customizing the Message Broker
+Spring Cloud Bus uses
+Spring Cloud Stream to
+broadcast the messages so to get messages to flow you only need to
+include the binder implementation of your choice in the
+classpath. There are convenient starters specifically for the bus with
+AMQP, Kafka and Redis
+(spring-cloud-starter-bus-[amqp,kafka,redis]). Generally speaking
+Spring Cloud Stream relies on Spring Boot autoconfiguration
+conventions for configuring middleware, so for instance the AMQP
+broker address can be changed with spring.rabbitmq.*
+configuration properties. Spring Cloud Bus has a handful of native
+configuration properties in spring.cloud.bus.*
+(e.g. spring.cloud.bus.destination is the name of the topic to use
+the the externall middleware). Normally the defaults will suffice.
To lean more about how to customize the message broker settings +consult the Spring Cloud Stream documentation.
+Tracing Bus Events
+Bus events (subclasses of RemoteApplicationEvent) can be traced by
+setting spring.cloud.bus.trace.enabled=true. If you do this then the
+Spring Boot TraceRepository (if it is present) will show each event
+sent and all the acks from each service instance. Example (from the
+/trace endpoint):
{
+ "timestamp": "2015-11-26T10:24:44.411+0000",
+ "info": {
+ "signal": "spring.cloud.bus.ack",
+ "type": "RefreshRemoteApplicationEvent",
+ "id": "c4d374b7-58ea-4928-a312-31984def293b",
+ "origin": "stores:8081",
+ "destination": "*:**"
+ }
+ },
+ {
+ "timestamp": "2015-11-26T10:24:41.864+0000",
+ "info": {
+ "signal": "spring.cloud.bus.sent",
+ "type": "RefreshRemoteApplicationEvent",
+ "id": "c4d374b7-58ea-4928-a312-31984def293b",
+ "origin": "customers:9000",
+ "destination": "*:**"
+ }
+ },
+ {
+ "timestamp": "2015-11-26T10:24:41.862+0000",
+ "info": {
+ "signal": "spring.cloud.bus.ack",
+ "type": "RefreshRemoteApplicationEvent",
+ "id": "c4d374b7-58ea-4928-a312-31984def293b",
+ "origin": "customers:9000",
+ "destination": "*:**"
+ }
+}This trace shows that a RefreshRemoteApplicationEvent was sent from
+customers:9000, broadcast to all services, and it was received
+(acked) by customers:9000 and stores:8081.
To handle the ack signals yourself you could add an @EventListener
+for the AckRemoteAppplicationEvent and SentApplicationEvent types
+to your app (and enable tracing). Or you could tap into the
+TraceRepository and mine the data from there.
|
+ Note
+ |
++Any Bus application can trace acks, but sometimes it will be +useful to do this in a central service that can do more complex +queries on the data. Or forward it to a specialized tracing service. + | +
Spring Boot Cloud CLI
+Spring Boot CLI provides Spring Boot command line features for
+Spring Cloud. You can write Groovy scripts to run Spring Cloud component applications
+(e.g. @EnableEurekaServer). You can also easily do things like encryption and decryption to support Spring Cloud
+Config clients with secret configuration values.
Installation
+To install, make +sure you have +Spring Boot CLI +(1.2.0 or better):
+$ spring version +Spring CLI v1.2.3.RELEASE+
E.g. for GVM users
+$ gvm install springboot 1.3.0.M5
+$ gvm use springboot 1.3.0.M5and install the Spring Cloud plugin:
+$ mvn install
+$ spring install org.springframework.cloud:spring-cloud-cli:1.1.0.BUILD-SNAPSHOT|
+ Important
+ |
++Prerequisites: to use the encryption and decryption features +you need the full-strength JCE installed in your JVM (it’s not there by default). +You can download the "Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files" +from Oracle, and follow instructions for installation (essentially replace the 2 policy files +in the JRE lib/security directory with the ones that you downloaded). + | +
Writing Groovy Scripts and Running Applications
+Spring Cloud CLI has support for most of the Spring Cloud declarative
+features, such as the @Enable* class of annotations. For example,
+here is a fully functional Eureka server
@EnableEurekaServer
+class Eureka {}which you can run from the command line like this
+$ spring run app.groovy+
To include additional dependencies, often it suffices just to add the
+appropriate feature-enabling annotation, e.g. @EnableConfigServer,
+@EnableOAuth2Sso or @EnableEurekaClient. To manually include a
+dependency you can use a @Grab with the special "Spring Boot" short
+style artifact co-ordinates, i.e. with just the artifact ID (no need
+for group or version information), e.g. to set up a client app to
+listen on AMQP for management events from the Spring CLoud Bus:
@Grab('spring-cloud-starter-bus-amqp')
+@RestController
+class Service {
+ @RequestMapping('/')
+ def home() { [message: 'Hello'] }
+}Encryption and Decryption
+The Spring Cloud CLI comes with an "encrypt" and a "decrypt" +command. Both accept arguments in the same form with a key specified +as a mandatory "--key", e.g.
+$ spring encrypt mysecret --key foo +682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda +$ spring decrypt --key foo 682bc583f4641835fa2db009355293665d2647dade3375c0ee201de2a49f7bda +mysecret+
To use a key in a file (e.g. an RSA public key for encyption) prepend +the key value with "@" and provide the file path, e.g.
+$ spring encrypt mysecret --key @${HOME}/.ssh/id_rsa.pub
+AQAjPgt3eFZQXwt8tsHAVv/QHiY5sI2dRcR+...
+Spring Cloud Security
+Spring Cloud Security offers a set of primitives for building secure +applications and services with minimum fuss. A declarative model which +can be heavily configured externally (or centrally) lends itself to +the implementation of large systems of co-operating, remote components, +usually with a central indentity management service. It is also extremely +easy to use in a service platform like Cloud Foundry. Building on +Spring Boot and Spring Security OAuth2 we can quickly create systems that +implement common patterns like single sign on, token relay and token +exchange.
+Quickstart
+OAuth2 Single Sign On
+Here’s a Spring Cloud "Hello World" app with HTTP Basic +authentication and a single user account:
+@Grab('spring-boot-starter-security')
+@Controller
+class Application {
+
+ @RequestMapping('/')
+ String home() {
+ 'Hello World'
+ }
+
+}You can run it with spring run app.groovy and watch the logs for the password (username is "user"). So far this is just the default for a Spring Boot app.
Here’s a Spring Cloud app with OAuth2 SSO:
+@Controller
+@EnableOAuth2Sso
+class Application {
+
+ @RequestMapping('/')
+ String home() {
+ 'Hello World'
+ }
+
+}Spot the difference? This app will actually behave exactly the same as +the previous one, because it doesn’t know it’s OAuth2 credentals +yet.
+You can register an app in github quite easily, so try that if you +want a production app on your own domain. If you are happy to test on +localhost:8080, then set up these properties in your application +configuration:
+spring:
+ oauth2:
+ client:
+ clientId: bd1c0a783ccdd1c9b9e4
+ clientSecret: 1a9030fbca47a5b2c28e92f19050bb77824b5ad1
+ accessTokenUri: https://github.com/login/oauth/access_token
+ userAuthorizationUri: https://github.com/login/oauth/authorize
+ clientAuthenticationScheme: form
+ resource:
+ userInfoUri: https://api.github.com/user
+ preferTokenInfo: falserun the app above and it will redirect to github for authorization. If +you are already signed into github you won’t even notice that it has +authenticated. These credentials will only work if your app is +running on port 8080.
+To limit the scope that the client asks for when it obtains an access token
+you can set spring.oauth2.client.scope (comma separated or an array in YAML). By
+default the scope is empty and it is up to to Authorization Server to
+decide what the defaults should be, usually depending on the settings in
+the client registration that it holds.
|
+ Note
+ |
++The examples above are all Groovy scripts. If you want to write the +same code in Java (or Groovy) you need to add Spring Security OAuth2 +to the classpath (e.g. see the +sample here). + | +
OAuth2 Protected Resource
+You want to protect an API resource with an OAuth2 token? Here’s a +simple example (paired with the client above):
+@Grab('spring-cloud-starter-security')
+@RestController
+@EnableResourceServer
+class Application {
+
+ @RequestMapping('/')
+ def home() {
+ [message: 'Hello World']
+ }
+
+}and
+spring:
+ oauth2:
+ resource:
+ userInfoUri: https://api.github.com/user
+ preferTokenInfo: falseMore Detail
+Single Sign On
+|
+ Note
+ |
++All of the OAuth2 SSO and resource server features moved to Spring Boot +in version 1.3. You can find documentation in the +Spring Boot user guide. + | +
Token Relay
+A Token Relay is where an OAuth2 consumer acts as a Client and +forwards the incoming token to outgoing resource requests. The +consumer can be a pure Client (like an SSO application) or a Resource +Server.
+Client Token Relay
+If your app has a
+Spring
+Cloud Zuul embedded reverse proxy (using @EnableZuulProxy) then you
+can ask it to forward OAuth2 access tokens downstream to the services
+it is proxying. Thus the SSO app above can be enhanced simply like this:
@Controller
+@EnableOAuth2Sso
+@EnableZuulProxy
+class Application {
+
+}and it will (in addition to loggin the user in and grabbing a token)
+pass the authentication token downstream to the /proxy/*
+services. If those services are implemented with
+@EnableOAuth2Resource then they will get a valid token in the
+correct header.
How does it work? The @EnableOAuth2Sso annotation pulls in
+spring-cloud-starter-security (which you could do manually in a
+traditional app), and that in turn triggers some autoconfiguration for
+a ZuulFilter, which itself is activated because Zuul is on the
+classpath (via @EnableZuulProxy). The
+filter
+just extracts an access token from the currently authenticated user,
+and puts it in a request header for the downstream requests.
Resource Server Token Relay
+If your app has @EnableOAuth2Resource and also is a Client (i.e. it
+has a spring.oauth2.client.clientId, even if it doesn’t use it),
+then the OAuth2RestOperations that is provided for @Autowired
+users by Spring Cloud (it is declared as @Primary) will also forward
+tokens. If you don’t want to forward tokens (and that is a valid
+choice, since you might want to act as yourself, rather than the
+client that sent you the token), then you only need to create your own
+OAuth2RestOperations instead of autowiring the default one. Here’s
+a basic example showing the use of the autowired rest template ("foo.com"
+is a Resource Server accepting the same tokens as the surrounding app):
@Autowired
+private OAuth2RestOperations restTemplate;
+
+@RequestMapping("/relay")
+public String relay() {
+ ResponseEntity<String> response =
+ restTemplate.getForEntity("https://foo.com/bar", String.class);
+ return "Success! (" + response.getBody() + ")";
+}Configuring Authentication Downstream of a Zuul Proxy
+You can control the authorization behaviour downstream of an
+@EnableZuulProxy through the proxy.auth.* settings. Example:
proxy:
+ auth:
+ routes:
+ customers: oauth2
+ stores: passthru
+ recommendations: noneIn this example the "customers" service gets an OAuth2 token relay, +the "stores" service gets a passthrough (the authorization header is +just passed downstream), and the "recommendations" service has its +authorization header removed. The default behaviour is to do a token +relay if there is a token available, and passthru otherwise.
+See + +ProxyAuthenticationProperties for full details.
+