This project provides Netflix OSS integrations for Spring Boot apps through autoconfiguration +and binding to the Spring Environment and other Spring programming model idioms. With a few +simple annotations you can quickly enable and configure the common patterns inside your +application and build large distributed systems with battle-tested Netflix components. The +patterns provided include Service Discovery (Eureka), Circuit Breaker (Hystrix), +Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon).
+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.contextPath}/info
+ healthCheckUrlPath: ${management.contextPath}/health
+These links show up in the metadata that is consumers by clients, and +used in some scenarios to decide whether to send requests to your +application, so it’s helpful if they are accurate.
+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). For example:
+eureka:
+ instance:
+ hostname: ${vcap.application.uris[0]}
+ nonSecurePort: 80
+ metadataMap:
+ instanceId: ${vcap.application.instance_id:${spring.application.name}:${spring.application.instance_id:${server.port}}}
+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;
+}Making the Eureka Instance ID Unique
+By default a eureka instance is registered with an ID that is equal to its host name (i.e. only one service per host). Using Spring Cloud you can override this by providing a unique identifier in eureka.instance.metadataMap.instanceId. For example:
eureka:
+ instance:
+ metadataMap:
+ 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 DiscoveryClient
+Once you have an app that is @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.DiscoveryClient (as opposed to the Spring
+Cloud DiscoveryClient), e.g.
@Autowired
+private DiscoveryClient discoveryClient;
+
+public String serviceUrl() {
+ InstanceInfo instance = discoveryClient.getNextServerFromEureka("STORES", false);
+ return instance.getHomePageUrl();
+}
+|
+ Tip
+ |
+
+
+
+Don’t use the |
+
Alternatives to the native Netflix DiscoveryClient
+You don’t have to use the raw Netflix DiscoveryClient 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.
In particular you might be interested
+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 approximateZoneFromDomain 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(@PathParameter("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).
+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.comTo 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 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.
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-samples