diff --git a/multi/multi_pr01.html b/multi/multi_pr01.html index 0e42f128..abf6918c 100644 --- a/multi/multi_pr01.html +++ b/multi/multi_pr01.html @@ -1,9 +1,9 @@ -
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This project provides Zookeeper 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 Zookeeper based components. The -patterns provided include Service Discovery and Configuration. -Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Breaker -(Hystrix) are provided by integration with Spring Cloud Netflix.

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Spring Cloud Zookeeper Home 1. Install Zookeeper
\ No newline at end of file +
Prev   Next

This project provides Zookeeper integrations for Spring Boot applications through +autoconfiguration and binding to the Spring Environment and other Spring programming model +idioms. With a few annotations, you can quickly enable and configure the common patterns +inside your application and build large distributed systems with Zookeeper based +components. The provided patterns include Service Discovery and Configuration. Integration +with Spring Cloud Netflix provides Intelligent Routing (Zuul), Client Side Load Balancing +(Ribbon), and Circuit Breaker (Hystrix).

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Spring Cloud Zookeeper Home 1. Install Zookeeper
\ No newline at end of file diff --git a/multi/multi_spring-cloud-zookeeper-config.html b/multi/multi_spring-cloud-zookeeper-config.html index 42429425..f9824035 100644 --- a/multi/multi_spring-cloud-zookeeper-config.html +++ b/multi/multi_spring-cloud-zookeeper-config.html @@ -1,9 +1,23 @@ - 7. Distributed Configuration with Zookeeper
7. Distributed Configuration with Zookeeper
Prev   

7. Distributed Configuration with Zookeeper

Zookeeper provides a hierarchical namespace that allows clients to store arbitrary data, such as configuration data. Spring Cloud Zookeeper Config is an alternative to the Config Server and Client. Configuration is loaded into the Spring Environment during the special "bootstrap" phase. Configuration is stored in the /config namespace by default. Multiple PropertySource instances are created based on the application’s name and the active profiles that mimicks the Spring Cloud Config order of resolving properties. For example, an application with the name "testApp" and with the "dev" profile will have the following property sources created:

config/testApp,dev
-config/testApp
-config/application,dev
-config/application

The most specific property source is at the top, with the least specific at the bottom. Properties is the config/application namespace are applicable to all applications using zookeeper for configuration. Properties in the config/testApp namespace are only available to the instances of the service named "testApp".

Configuration is currently read on startup of the application. Sending a HTTP POST to /refresh will cause the configuration to be reloaded. Watching the configuration namespace (which Zookeeper supports) is not currently implemented, but will be a future addition to this project.

7.1 How to activate

Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-config will enable auto-configuration that will setup Spring Cloud Zookeeper Config.

7.2 Customizing

Zookeeper Config may be customized using the following properties:

bootstrap.yml.  + 7. Distributed Configuration with Zookeeper

7. Distributed Configuration with Zookeeper
Prev   

7. Distributed Configuration with Zookeeper

Zookeeper provides a +hierarchical namespace +that lets clients store arbitrary data, such as configuration data. Spring Cloud Zookeeper +Config is an alternative to the +Config Server and Client. +Configuration is loaded into the Spring Environment during the special “bootstrap” +phase. Configuration is stored in the /config namespace by default. Multiple +PropertySource instances are created, based on the application’s name and the active +profiles, to mimic the Spring Cloud Config order of resolving properties. For example, an +application with a name of testApp and with the dev profile has the following property +sources created for it:

  • config/testApp,dev
  • config/testApp
  • config/application,dev
  • config/application

The most specific property source is at the top, with the least specific at the bottom. +Properties in the config/application namespace apply to all applications that use +zookeeper for configuration. Properties in the config/testApp namespace are available +only to the instances of the service named testApp.

Configuration is currently read on startup of the application. Sending a HTTP POST +request to /refresh causes the configuration to be reloaded. Watching the configuration +namespace (which Zookeeper supports) is not currently implemented.

7.1 Activating

Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-config enables +autoconfiguration that sets up Spring Cloud Zookeeper Config.

7.2 Customizing

Zookeeper Config may be customized by setting the following properties:

bootstrap.yml.  

spring:
   cloud:
     zookeeper:
@@ -12,8 +26,10 @@ config/application

The most specific property source is at the top, with root: configuration defaultContext: apps profileSeparator: '::'

-

  • enabled setting this value to "false" disables Zookeeper Config
  • root sets the base namespace for configuration values
  • defaultContext sets the name used by all applications
  • profileSeparator sets the value of the separator used to separate the profile name in property sources with profiles

7.3 ACLs

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo method of a -CuratorFramework bean. One way to accomplish this is by providing your own CuratorFramework bean:

@BoostrapConfiguration
+
  • enabled: Setting this value to false disables Zookeeper Config.
  • root: Sets the base namespace for configuration values.
  • defaultContext: Sets the name used by all applications.
  • profileSeparator: Sets the value of the separator used to separate the profile name in
+property sources with profiles.

7.3 Access Control Lists (ACLs)

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo +method of a CuratorFramework bean. One way to accomplish this is to provide your own +CuratorFramework bean, as shown in the following example:

@BoostrapConfiguration
 public class CustomCuratorFrameworkConfig {
 
   @Bean
@@ -23,20 +39,21 @@ CuratorFramework bean. One way to accomplish this is by providing your own Curat
     return curator;
   }
 
-}

Consult the ZookeeperAutoConfiguration class -to see how the CuratorFramework bean is configured by default.

Alternatively, you can add your credentials from a class that depends on the existing -CuratorFramework bean:

@BoostrapConfiguration
+}

Consult +the ZookeeperAutoConfiguration class +to see how the CuratorFramework bean’s default configuration.

Alternatively, you can add your credentials from a class that depends on the existing +CuratorFramework bean, as shown in the following example:

@BoostrapConfiguration
 public class DefaultCuratorFrameworkConfig {
 
   public ZookeeperConfig(CuratorFramework curator) {
     curator.addAuthInfo("digest", "user:password".getBytes());
   }
 
-}

This must occur during the boostrapping phase. You can register configuration classes to run -during this phase by annotating them with @BootstrapConfiguration and including them in a -comma-separated list set as the value of the property -org.springframework.cloud.bootstrap.BootstrapConfiguration in the file -resources/META-INF/spring.factories:

resources/META-INF/spring.factories.  +}

The creation of this bean must occur during the boostrapping phase. You can register +configuration classes to run during this phase by annotating them with +@BootstrapConfiguration and including them in a comma-separated list that you set as the +value of the org.springframework.cloud.bootstrap.BootstrapConfiguration property in the +resources/META-INF/spring.factories file, as shown in the following example:

resources/META-INF/spring.factories.  

org.springframework.cloud.bootstrap.BootstrapConfiguration=\
 my.project.CustomCuratorFrameworkConfig,\
 my.project.DefaultCuratorFrameworkConfig

diff --git a/multi/multi_spring-cloud-zookeeper-dependencies.html b/multi/multi_spring-cloud-zookeeper-dependencies.html index b7923674..69b03665 100644 --- a/multi/multi_spring-cloud-zookeeper-dependencies.html +++ b/multi/multi_spring-cloud-zookeeper-dependencies.html @@ -1,8 +1,15 @@ - 5. Zookeeper Dependencies

5. Zookeeper Dependencies
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5. Zookeeper Dependencies

5.1 Using the Zookeeper Dependencies

Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application as properties. As dependencies you can understand other applications that are registered -in Zookeeper and which you would like to call via Feign (a REST client builder) -and also Spring RestTemplate.

You can also benefit from the Zookeeper Dependency Watchers functionality that lets you control and monitor what is the state of your dependencies and decide what to do with that.

5.2 How to activate Zookeeper Dependencies

  • Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Dependencies.
  • If you have to have the spring.cloud.zookeeper.dependencies section properly set up - check the subsequent section for more details then the feature is active
  • You can have the dependencies turned off even if you’ve provided the dependencies in your properties. Just set the property spring.cloud.zookeeper.dependency.enabled to false (defaults to true).

5.3 Setting up Zookeeper Dependencies

Let’s take a closer look at an example of dependencies representation:

application.yml.  + 5. Zookeeper Dependencies

5. Zookeeper Dependencies
Prev   Next

5. Zookeeper Dependencies

The following topics cover how to work with Spring Cloud Zookeeper dependencies:

5.1 Using the Zookeeper Dependencies

Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application +as properties. As dependencies, you can understand other applications that are registered +in Zookeeper and which you would like to call through +Feign +(a REST client builder) and Spring RestTemplate.

You can also use the Zookeeper Dependency Watchers functionality to control and monitor +the state of your dependencies.

5.2 Activating Zookeeper Dependencies

Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables +autoconfiguration that sets up Spring Cloud Zookeeper Dependencies. Even if you provide +the dependencies in your properties, you can turn off the dependencies. To do so, set the +spring.cloud.zookeeper.dependency.enabled property to false (it defaults to true).

5.3 Setting up Zookeeper Dependencies

Consider the following example of dependency representation:

application.yml.  

spring.application.name: yourServiceName
 spring.cloud.zookeeper:
   dependencies:
@@ -24,25 +31,56 @@ spring.cloud.zookeeper:
       contentTypeTemplate: application/vnd.mailing.$version+json
       version: v1
       required: true

-

Let’s now go through each part of the dependency one by one. The root property name is spring.cloud.zookeeper.dependencies.

5.3.1 Aliases

Below the root property you have to represent each dependency has by an alias due to the constraints of Ribbon (the application id has to be placed in the URL -thus you can’t pass any complex path like /foo/bar/name). The alias will be the name that you will use instead of serviceId for DiscoveryClient, Feign or RestTemplate.

In the aforementioned examples the aliases are newsletter and mailing. Example of Feign usage with newsletter would be:

@FeignClient("newsletter")
+
The next few sections go through each part of the dependency one by one. The root property
+name is spring.cloud.zookeeper.dependencies.
5.3.1 Aliases
Below the root property you have to represent each dependency as an alias. This is due to
+the constraints of Ribbon, which requires that the application ID be placed in the URL.
+Consequently, you cannot pass any complex path, suchas  /myApp/myRoute/name). The alias
+is the name you use instead of the serviceId for DiscoveryClient, Feign, or
+RestTemplate.
In the previous examples, the aliases are newsletter and mailing. The following
+example shows Feign usage with a newsletter alias:
@FeignClient("newsletter")
 public interface NewsletterService {
         @RequestMapping(method = RequestMethod.GET, value = "/newsletter")
         String getNewsletters();
-}
5.3.2 Path
Represented by path yaml property.
Path is the path under which the dependency is registered under Zookeeper. Like presented before Ribbon operates on URLs thus this path is not compliant with its requirement.
-That is why Spring Cloud Zookeeper maps the alias to the proper path.
5.3.3 Load balancer type
Represented by loadBalancerType yaml property.
If you know what kind of load balancing strategy has to be applied when calling this particular dependency then you can provide it in the yaml file and it will be automatically applied.
-You can choose one of the following load balancing strategies
  • STICKY - once chosen the instance will always be called
  • RANDOM - picks an instance randomly
  • ROUND_ROBIN - iterates over instances over and over again
5.3.4 Content-Type template and version
Represented by contentTypeTemplate and version yaml property.
If you version your api via the Content-Type header then you don’t want to add this header to each of your requests. Also if you want to call a new version of the API you don’t want to
-roam around your code to bump up the API version. That’s why you can provide a contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the
-version yaml property. Let’s take a look at an example.
Having the following contentTypeTemplate:
application/vnd.newsletter.$version+json
and the following version:
v1
Will result in setting up of a Content-Type header for each request:
application/vnd.newsletter.v1+json
5.3.5 Default headers
Represented by headers map in yaml
Sometimes each call to a dependency requires setting up of some default headers. In order not to do that in code you can set them up in the yaml file.
-Having the following headers section:
headers:
+}
5.3.2 Path
The path is represented by the path YAML property and is the path under which the
+dependency is registered under Zookeeper. As described in the
+previous section, Ribbon
+operates on URLs. As a result, this path is not compliant with its requirement.
+That is why Spring Cloud Zookeeper maps the alias to the proper path.
5.3.3 Load Balancer Type
The load balancer type is represented by loadBalancerType YAML property.
If you know what kind of load-balancing strategy has to be applied when calling this
+particular dependency, you can provide it in the YAML file, and it is automatically
+applied. You can choose one of the following load balancing strategies:
  • STICKY: Once chosen, the instance is always called.
  • RANDOM: Picks an instance randomly.
  • ROUND_ROBIN: Iterates over instances over and over again.
5.3.4 Content-Type Template and Version
The Content-Type template and version are represented by the contentTypeTemplate and
+version YAML properties.
If you version your API in the Content-Type header, you do not want to add this header
+to each of your requests. Also, if you want to call a new version of the API, you do not
+want to roam around your code to bump up the API version. That is why you can provide a
+contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the
+version YAML property. Consider the following example of a contentTypeTemplate:
application/vnd.newsletter.$version+json
Further consider the following version:
v1
The combination of contentTypeTemplate and version results in the creation of a
+Content-Type header for each request, as follows:
application/vnd.newsletter.v1+json
5.3.5 Default Headers
Default headers are represented by the headers map in YAML.
Sometimes, each call to a dependency requires setting up of some default headers. To not
+do that in code, you can set them up in the YAML file, as shown in the following example
+headers section:
headers:
     Accept:
         - text/html
         - application/xhtml+xml
     Cache-Control:
-        - no-cache
Results in adding the Accept and Cache-Control headers with appropriate list of values in your HTTP request.
5.3.6 Obligatory dependencies
Represented by required property in yaml
If one of your dependencies is required to be up and running when your application is booting then it’s enough to set up the required: true property in the yaml file.
If your application can’t localize the required dependency during boot time it will throw an exception and the Spring Context will fail to set up.
-In other words your application won’t be able to start if the required dependency is not registered in Zookeeper.
You can read more about Spring Cloud Zookeeper Presence Checker in the following sections.
5.3.7 Stubs
You can provide a colon separated path to the JAR containing stubs of the dependency. Example
stubs: org.springframework:foo:stubs
means that for a particular dependencies can be found under:
  • groupId: org.springframework
  • artifactId: foo
  • classifier: stubs - this is the default value
This is actually equal to
stubs: org.springframework:foo
since stubs is the default classifier.

5.4 Configuring Spring Cloud Zookeeper Dependencies

There is a bunch of properties that you can set to enable / disable parts of Zookeeper Dependencies functionalities.

  • spring.cloud.zookeeper.dependencies - if you don’t set this property you won’t benefit from Zookeeper Dependencies
  • spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default) - Ribbon requires explicit global configuration or a particular one for a dependency. By turning on this property -runtime load balancing strategy resolution is possible and you can profit from the loadBalancerType section of the Zookeeper Dependencies. The configuration that needs this property -has an implementation of LoadBalancerClient that delegates to the ILoadBalancer presented in the next bullet
  • spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default) - thanks to this property the custom ILoadBalancer knows that the part of the URI passed to Ribbon might -actually be the alias that has to be resolved to a proper path in Zookeeper. Without this property you won’t be able to register applications under nested paths.
  • spring.cloud.zookeeper.dependency.headers.enabled (enabled by default) - this property registers such a RibbonClient that automatically will append appropriate headers and content -types with version as presented in the Dependency configuration. Without this setting of those two parameters will not be operational.
  • spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default) - when enabled will modify the request headers of @LoadBalanced annotated RestTemplate so that it passes -headers and content type with version set in Dependency configuration. Wihtout this setting of those two parameters will not be operational.
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4. Spring Cloud Zookeeper and Service Registry Home 6. Spring Cloud Zookeeper Dependency Watcher
\ No newline at end of file + - no-cache

That headers section results in adding the Accept and Cache-Control headers with +appropriate list of values in your HTTP request.

5.3.6 Required Dependencies

Required dependencies are represented by required property in YAML.

If one of your dependencies is required to be up when your application boots, you can set +the required: true property in the YAML file.

If your application cannot localize the required dependency during boot time, it throws an +exception, and the Spring Context fails to set up. In other words, your application cannot +start if the required dependency is not registered in Zookeeper.

You can read more about Spring Cloud Zookeeper Presence Checker +later in this document.

5.3.7 Stubs

You can provide a colon-separated path to the JAR containing stubs of the dependency, as +shown in the following example:

stubs: org.springframework:myApp:stubs

where:

  • org.springframework is the groupId.
  • myApp is the artifactId.
  • stubs is the classifier. (Note that stubs is the default value.)

Because stubs is the default classifier, the preceding example is equal to the following +example:

stubs: org.springframework:myApp

5.4 Configuring Spring Cloud Zookeeper Dependencies

You can set the following properties to enable or disable parts of Zookeeper Dependencies +functionalities:

  • spring.cloud.zookeeper.dependencies: If you do not set this property, you cannot use +Zookeeper Dependencies.
  • spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default): Ribbon requires +either explicit global configuration or a particular one for a dependency. By turning on +this property, runtime load balancing strategy resolution is possible, and you can use the +loadBalancerType section of the Zookeeper Dependencies. The configuration that needs +this property has an implementation of LoadBalancerClient that delegates to the +ILoadBalancer presented in the next bullet.
  • spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default): Thanks to +this property, the custom ILoadBalancer knows that the part of the URI passed to Ribbon +might actually be the alias that has to be resolved to a proper path in Zookeeper. Without +this property, you cannot register applications under nested paths.
  • spring.cloud.zookeeper.dependency.headers.enabled (enabled by default): This property +registers a RibbonClient that automatically appends appropriate headers and content +types with their versions, as presented in the Dependency configuration. Without this +setting, those two parameters do not work.
  • spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default): When +enabled, this property modifies the request headers of a @LoadBalanced-annotated +RestTemplate such that it passes headers and content type with the version set in +dependency configuration. Without this setting, those two parameters do not work.
Prev   Next
4. Spring Cloud Zookeeper and Service Registry Home 6. Spring Cloud Zookeeper Dependency Watcher
\ No newline at end of file diff --git a/multi/multi_spring-cloud-zookeeper-dependency-watcher.html b/multi/multi_spring-cloud-zookeeper-dependency-watcher.html index ed00ff8a..534a0659 100644 --- a/multi/multi_spring-cloud-zookeeper-dependency-watcher.html +++ b/multi/multi_spring-cloud-zookeeper-dependency-watcher.html @@ -1,8 +1,21 @@ - 6. Spring Cloud Zookeeper Dependency Watcher
6. Spring Cloud Zookeeper Dependency Watcher
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6. Spring Cloud Zookeeper Dependency Watcher

The Dependency Watcher mechanism allows you to register listeners to your dependencies. The functionality is in fact an implementation of the Observator pattern. When a dependency changes -its state (UP or DOWN) then some custom logic can be applied.

6.1 How to activate

Spring Cloud Zookeeper Dependencies functionality needs to be enabled to profit from Dependency Watcher mechanism.

6.2 Registering a listener

In order to register a listener you have to implement an interface org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and register it as a bean. -The interface gives you one method:

void stateChanged(String dependencyName, DependencyState newState);

If you want to register a listener for a particular dependency then the dependencyName would be the discriminator for your concrete implementation. newState will provide you with information - whether your dependency has changed to CONNECTED or DISCONNECTED.

6.3 Presence Checker

Bound with Dependency Watcher is the functionality called Presence Checker. It allows you to provide custom behaviour upon booting of your application to react accordingly to the state -of your dependencies.

The default implementation of the abstract org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier class is the -org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier which works in the following way.

  • If the dependency is marked us required and it’s not in Zookeeper then upon booting your application will throw an exception and shutdown
  • If dependency is not required the org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker will log that application is missing at WARN level

The functionality can be overridden since the DefaultDependencyPresenceOnStartupVerifier is registered only when there is no bean of DependencyPresenceOnStartupVerifier.

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5. Zookeeper Dependencies Home 7. Distributed Configuration with Zookeeper
\ No newline at end of file + 6. Spring Cloud Zookeeper Dependency Watcher
6. Spring Cloud Zookeeper Dependency Watcher
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6. Spring Cloud Zookeeper Dependency Watcher

The Dependency Watcher mechanism lets you register listeners to your dependencies. The +functionality is, in fact, an implementation of the Observator pattern. When a +dependency changes, its state (to either UP or DOWN), some custom logic can be applied.

6.1 Activating

Spring Cloud Zookeeper Dependencies functionality needs to be enabled for you to use the +Dependency Watcher mechanism.

6.2 Registering a Listener

To register a listener, you must implement an interface called +org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and +register it as a bean. The interface gives you one method:

void stateChanged(String dependencyName, DependencyState newState);

If you want to register a listener for a particular dependency, the dependencyName would +be the discriminator for your concrete implementation. newState provides you with +information about whether your dependency has changed to CONNECTED or DISCONNECTED.

6.3 Using the Presence Checker

Bound with the Dependency Watcher is the functionality called Presence Checker. It lets +you provide custom behavior when your application boots, to react according to the state +of your dependencies.

The default implementation of the abstract +org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier +class is the +org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier, +which works in the following way.

  1. If the dependency is marked us required and is not in Zookeeper, when your application +boots, it throws an exception and shuts down.
  2. If the dependency is not required, the +org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker +logs that the dependency is missing at the WARN level.

Because the DefaultDependencyPresenceOnStartupVerifier is registered only when there is +no bean of type DependencyPresenceOnStartupVerifier, this functionality can be +overridden.

Prev   Next
5. Zookeeper Dependencies Home 7. Distributed Configuration with Zookeeper
\ No newline at end of file diff --git a/multi/multi_spring-cloud-zookeeper-discovery.html b/multi/multi_spring-cloud-zookeeper-discovery.html index 052db725..3e23db2d 100644 --- a/multi/multi_spring-cloud-zookeeper-discovery.html +++ b/multi/multi_spring-cloud-zookeeper-discovery.html @@ -1,6 +1,15 @@ - 2. Service Discovery with Zookeeper
2. Service Discovery with Zookeeper
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2. Service Discovery with Zookeeper

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. Curator(A java library for Zookeeper) provides Service Discovery services via Service Discovery Extension. Spring Cloud Zookeeper leverages this extension for service registration and discovery.

2.1 How to activate

Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Discovery.

[Note]Note

You still need to include org.springframework.boot:spring-boot-starter-web for web functionality.

2.2 Registering with Zookeeper

When a client registers with Zookeeper, it provides meta-data about itself such as host and port, id and name.

Example Zookeeper client:

@SpringBootApplication
+   2. Service Discovery with Zookeeper
2. Service Discovery with Zookeeper
Prev   Next
2. Service Discovery with Zookeeper
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 difficult to do and can be
+brittle. Curator(A Java library for Zookeeper) provides Service
+Discovery through a Service Discovery
+Extension. Spring Cloud Zookeeper uses this extension for service registration and
+discovery.
2.1 Activating
Including a dependency on
+org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables
+autoconfiguration that sets up Spring Cloud Zookeeper Discovery.
[Note]Note
For web functionality, you still need to include
+org.springframework.boot:spring-boot-starter-web.
2.2 Registering with Zookeeper
When a client registers with Zookeeper, it provides metadata (such as host and port, ID,
+and name) about itself.
The following example shows a Zookeeper client:
@SpringBootApplication
 @RestController
 public class Application {
 
@@ -13,12 +22,25 @@
         new SpringApplicationBuilder(Application.class).web(true).run(args);
     }
 
-}
(i.e. utterly normal Spring Boot app).  If Zookeeper is located somewhere other than localhost:2181, the configuration is required to locate the server. Example:
application.yml. 
+}
[Note]Note

The preceding example is a normal Spring Boot application.

If Zookeeper is located somewhere other than localhost:2181, the configuration must +provide the location of the server, as shown in the following example:

application.yml.  

spring:
   cloud:
     zookeeper:
       connect-string: localhost:2181

-

[Caution]Caution

If you use Spring Cloud Zookeeper Config, the above values will need to be placed in bootstrap.yml instead of application.yml.

The default service name, instance id and port, taken from the Environment, are ${spring.application.name}, the Spring Context ID and ${server.port} respectively.

Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both a Zookeeper "service" (i.e. it registers itself) and a "client" (i.e. it can query Zookeeper to locate other services).

If you would like to disable the Zookeeper Discovery Client you can set spring.cloud.zookeeper.discovery.enabled to false.

2.3 Using the DiscoveryClient

Spring Cloud has support for Feign (a REST client builder) and also Spring RestTemplate using the logical service names instead of physical URLs.

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
+
[Caution]Caution
If you use Spring Cloud Zookeeper Config, the
+values shown in the preceding example need to be in bootstrap.yml instead of
+application.yml.
The default service name, instance ID, and port (taken from the Environment) are
+${spring.application.name}, the Spring Context ID, and ${server.port}, respectively.
Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both
+a Zookeeper “service” (that is, it registers itself) and a “client” (that is, it can
+query Zookeeper to locate other services).
If you would like to disable the Zookeeper Discovery Client, you can set
+spring.cloud.zookeeper.discovery.enabled to false.

2.3 Using the DiscoveryClient

Spring Cloud has support for +Feign +(a REST client builder) and +Spring +RestTemplate, using logical service names instead of physical URLs.

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, as shown in +the following example:

@Autowired
 private DiscoveryClient discoveryClient;
 
 public String serviceUrl() {
diff --git a/multi/multi_spring-cloud-zookeeper-install.html b/multi/multi_spring-cloud-zookeeper-install.html
index 1f3b3b83..7ddac4c6 100644
--- a/multi/multi_spring-cloud-zookeeper-install.html
+++ b/multi/multi_spring-cloud-zookeeper-install.html
@@ -1,3 +1,4 @@
 
       
-   1. Install Zookeeper
1. Install Zookeeper
Prev   Next
1. Install Zookeeper
Please see the installation documentation for instructions on how to install Zookeeper.
Prev   Next
 Home 2. Service Discovery with Zookeeper

\ No newline at end of file
+   1. Install Zookeeper
1. Install Zookeeper
Prev   Next
1. Install Zookeeper
See the installation
+documentation for instructions on how to install Zookeeper.
Prev   Next
 Home 2. Service Discovery with Zookeeper

\ No newline at end of file
diff --git a/multi/multi_spring-cloud-zookeeper-netflix.html b/multi/multi_spring-cloud-zookeeper-netflix.html
index aa1b9b6d..36f5ced5 100644
--- a/multi/multi_spring-cloud-zookeeper-netflix.html
+++ b/multi/multi_spring-cloud-zookeeper-netflix.html
@@ -1,3 +1,7 @@
 
       
-   3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Prev   Next
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient implementation is used. Feign, Turbine, Ribbon and Zuul all work with Spring Cloud Zookeeper.
3.1 Ribbon with Zookeeper
Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When the spring-cloud-starter-zookeeper-discovery is used, Ribbon is auto-configured to use the ZookeeperServerList by default.
Prev   Next
2. Service Discovery with Zookeeper Home 4. Spring Cloud Zookeeper and Service Registry

\ No newline at end of file
+   3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Prev   Next
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient
+implementation you use. Feign, Turbine, Ribbon, and Zuul all work with Spring Cloud
+Zookeeper.
3.1 Ribbon with Zookeeper
Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When you use
+the  spring-cloud-starter-zookeeper-discovery, Ribbon is autoconfigured to use the
+ZookeeperServerList by default.
Prev   Next
2. Service Discovery with Zookeeper Home 4. Spring Cloud Zookeeper and Service Registry

\ No newline at end of file
diff --git a/multi/multi_spring-cloud-zookeeper-service-registry.html b/multi/multi_spring-cloud-zookeeper-service-registry.html
index c94ef656..fa41bdc5 100644
--- a/multi/multi_spring-cloud-zookeeper-service-registry.html
+++ b/multi/multi_spring-cloud-zookeeper-service-registry.html
@@ -1,6 +1,9 @@
 
       
-   4. Spring Cloud Zookeeper and Service Registry
4. Spring Cloud Zookeeper and Service Registry
Prev   Next
4. Spring Cloud Zookeeper and Service Registry
Spring Cloud Zookeeper implements the ServiceRegistry interface allowing developers to register arbitrary service in a programmatic way.
The ServiceInstanceRegistration class offers a builder() method to create a Registration object that can be used by the ServiceRegistry.
@Autowired
+   4. Spring Cloud Zookeeper and Service Registry
4. Spring Cloud Zookeeper and Service Registry
Prev   Next
4. Spring Cloud Zookeeper and Service Registry
Spring Cloud Zookeeper implements the ServiceRegistry interface, letting developers
+register arbitrary services in a programmatic way.
The ServiceInstanceRegistration class offers a builder() method to create a
+Registration object that can be used by the ServiceRegistry, as shown in the following
+example:
@Autowired
 private ZookeeperServiceRegistry serviceRegistry;
 
 public void registerThings() {
@@ -11,4 +14,13 @@
             .name("/a/b/c/d/anotherservice")
             .build();
     this.serviceRegistry.register(registration);
-}
4.1 Instance Status
Netflix Eureka supports having instances registered with the server that are OUT_OF_SERVICE and not returned as active service instances. This is very useful for behaviors such as blue/green deployments. The Curator Service Discovery recipe does not support this behavior. Taking advantage of the flexible payload has let Spring Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList filters out all non-null instance statuses that do not equal UP. If the instance status field is empty, it is considered UP for backwards compatibility. To change the status of an instance POST OUT_OF_SERVICE to the ServiceRegistry instance status actuator endpoint.
$ http POST http://localhost:8081/service-registry status=OUT_OF_SERVICE
NOTE: The above example uses the `http` command from https://httpie.org
Prev   Next
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components Home 5. Zookeeper Dependencies

\ No newline at end of file
+}
4.1 Instance Status
Netflix Eureka supports having instances that are OUT_OF_SERVICE registered with the
+server. These instances are not returned as active service instances. This is useful for
+behaviors such as blue/green deployments. (Note that the Curator Service Discovery recipe
+does not  support this behavior.) Taking advantage of the flexible payload has let Spring
+Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then
+filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList
+filters out all non-null instance statuses that do not equal UP. If the instance status
+field is empty, it is considered to be UP for backwards compatibility. To change the
+status of an instance, make a POST with OUT_OF_SERVICE to the ServiceRegistry
+instance status actuator endpoint, as shown in the following example:
$ http POST http://localhost:8081/service-registry status=OUT_OF_SERVICE
[Note]Note
The preceding example uses the http command from https://httpie.org.
Prev   Next
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components Home 5. Zookeeper Dependencies

\ No newline at end of file
diff --git a/multi/multi_spring-cloud-zookeeper.html b/multi/multi_spring-cloud-zookeeper.html
index 9593e15b..1a86ba6b 100644
--- a/multi/multi_spring-cloud-zookeeper.html
+++ b/multi/multi_spring-cloud-zookeeper.html
@@ -1,3 +1,3 @@
 
       
-   Spring Cloud Zookeeper
Spring Cloud Zookeeper
   Next
Spring Cloud Zookeeper
Table of Contents
1. Install Zookeeper
2. Service Discovery with Zookeeper
2.1. How to activate
2.2. Registering with Zookeeper
2.3. Using the DiscoveryClient
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3.1. Ribbon with Zookeeper
4. Spring Cloud Zookeeper and Service Registry
4.1. Instance Status
5. Zookeeper Dependencies
5.1. Using the Zookeeper Dependencies
5.2. How to activate Zookeeper Dependencies
5.3. Setting up Zookeeper Dependencies
5.3.1. Aliases
5.3.2. Path
5.3.3. Load balancer type
5.3.4. Content-Type template and version
5.3.5. Default headers
5.3.6. Obligatory dependencies
5.3.7. Stubs
5.4. Configuring Spring Cloud Zookeeper Dependencies
6. Spring Cloud Zookeeper Dependency Watcher
6.1. How to activate
6.2. Registering a listener
6.3. Presence Checker
7. Distributed Configuration with Zookeeper
7.1. How to activate
7.2. Customizing
7.3. ACLs
   Next
   

\ No newline at end of file
+   Spring Cloud Zookeeper
Spring Cloud Zookeeper
   Next
Spring Cloud Zookeeper
Table of Contents
1. Install Zookeeper
2. Service Discovery with Zookeeper
2.1. Activating
2.2. Registering with Zookeeper
2.3. Using the DiscoveryClient
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3.1. Ribbon with Zookeeper
4. Spring Cloud Zookeeper and Service Registry
4.1. Instance Status
5. Zookeeper Dependencies
5.1. Using the Zookeeper Dependencies
5.2. Activating Zookeeper Dependencies
5.3. Setting up Zookeeper Dependencies
5.3.1. Aliases
5.3.2. Path
5.3.3. Load Balancer Type
5.3.4. Content-Type Template and Version
5.3.5. Default Headers
5.3.6. Required Dependencies
5.3.7. Stubs
5.4. Configuring Spring Cloud Zookeeper Dependencies
6. Spring Cloud Zookeeper Dependency Watcher
6.1. Activating
6.2. Registering a Listener
6.3. Using the Presence Checker
7. Distributed Configuration with Zookeeper
7.1. Activating
7.2. Customizing
7.3. Access Control Lists (ACLs)
   Next
   

\ No newline at end of file
diff --git a/single/spring-cloud-zookeeper.html b/single/spring-cloud-zookeeper.html
index de77e3a8..ea690b32 100644
--- a/single/spring-cloud-zookeeper.html
+++ b/single/spring-cloud-zookeeper.html
@@ -1,12 +1,22 @@
 
       
-   Spring Cloud Zookeeper
Spring Cloud Zookeeper
Table of Contents
1. Install Zookeeper
2. Service Discovery with Zookeeper
2.1. How to activate
2.2. Registering with Zookeeper
2.3. Using the DiscoveryClient
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3.1. Ribbon with Zookeeper
4. Spring Cloud Zookeeper and Service Registry
4.1. Instance Status
5. Zookeeper Dependencies
5.1. Using the Zookeeper Dependencies
5.2. How to activate Zookeeper Dependencies
5.3. Setting up Zookeeper Dependencies
5.3.1. Aliases
5.3.2. Path
5.3.3. Load balancer type
5.3.4. Content-Type template and version
5.3.5. Default headers
5.3.6. Obligatory dependencies
5.3.7. Stubs
5.4. Configuring Spring Cloud Zookeeper Dependencies
6. Spring Cloud Zookeeper Dependency Watcher
6.1. How to activate
6.2. Registering a listener
6.3. Presence Checker
7. Distributed Configuration with Zookeeper
7.1. How to activate
7.2. Customizing
7.3. ACLs
This project provides Zookeeper 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 Zookeeper based components. The
-patterns provided include Service Discovery and Configuration.
-Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Breaker
-(Hystrix) are provided by integration with Spring Cloud Netflix.
1. Install Zookeeper
Please see the installation documentation for instructions on how to install Zookeeper.
2. Service Discovery with Zookeeper
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. Curator(A java library for Zookeeper) provides Service Discovery services via Service Discovery Extension. Spring Cloud Zookeeper leverages this extension for service registration and discovery.
2.1 How to activate
Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Discovery.
[Note]Note
You still need to include org.springframework.boot:spring-boot-starter-web for web functionality.
2.2 Registering with Zookeeper
When a client registers with Zookeeper, it provides meta-data about itself such as host and port, id and name.
Example Zookeeper client:
@SpringBootApplication
+   Spring Cloud Zookeeper
Spring Cloud Zookeeper
Table of Contents
1. Install Zookeeper
2. Service Discovery with Zookeeper
2.1. Activating
2.2. Registering with Zookeeper
2.3. Using the DiscoveryClient
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3.1. Ribbon with Zookeeper
4. Spring Cloud Zookeeper and Service Registry
4.1. Instance Status
5. Zookeeper Dependencies
5.1. Using the Zookeeper Dependencies
5.2. Activating Zookeeper Dependencies
5.3. Setting up Zookeeper Dependencies
5.3.1. Aliases
5.3.2. Path
5.3.3. Load Balancer Type
5.3.4. Content-Type Template and Version
5.3.5. Default Headers
5.3.6. Required Dependencies
5.3.7. Stubs
5.4. Configuring Spring Cloud Zookeeper Dependencies
6. Spring Cloud Zookeeper Dependency Watcher
6.1. Activating
6.2. Registering a Listener
6.3. Using the Presence Checker
7. Distributed Configuration with Zookeeper
7.1. Activating
7.2. Customizing
7.3. Access Control Lists (ACLs)
This project provides Zookeeper integrations for Spring Boot applications through
+autoconfiguration and binding to the Spring Environment and other Spring programming model
+idioms. With a few annotations, you can quickly enable and configure the common patterns
+inside your application and build large distributed systems with Zookeeper based
+components. The provided patterns include Service Discovery and Configuration. Integration
+with Spring Cloud Netflix provides Intelligent Routing (Zuul), Client Side Load Balancing
+(Ribbon), and Circuit Breaker (Hystrix).
1. Install Zookeeper
See the installation
+documentation for instructions on how to install Zookeeper.
2. Service Discovery with Zookeeper
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 difficult to do and can be
+brittle. Curator(A Java library for Zookeeper) provides Service
+Discovery through a Service Discovery
+Extension. Spring Cloud Zookeeper uses this extension for service registration and
+discovery.
2.1 Activating
Including a dependency on
+org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables
+autoconfiguration that sets up Spring Cloud Zookeeper Discovery.
[Note]Note
For web functionality, you still need to include
+org.springframework.boot:spring-boot-starter-web.
2.2 Registering with Zookeeper
When a client registers with Zookeeper, it provides metadata (such as host and port, ID,
+and name) about itself.
The following example shows a Zookeeper client:
@SpringBootApplication
 @RestController
 public class Application {
 
@@ -19,12 +29,25 @@ Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Brea
         new SpringApplicationBuilder(Application.class).web(true).run(args);
     }
 
-}
(i.e. utterly normal Spring Boot app).  If Zookeeper is located somewhere other than localhost:2181, the configuration is required to locate the server. Example:
application.yml. 
+}
[Note]Note
The preceding example is a normal Spring Boot application.
If Zookeeper is located somewhere other than localhost:2181, the configuration must
+provide the location of the server, as shown in the following example:
application.yml. 
 
spring:
   cloud:
     zookeeper:
       connect-string: localhost:2181

-
[Caution]Caution
If you use Spring Cloud Zookeeper Config, the above values will need to be placed in bootstrap.yml instead of application.yml.
The default service name, instance id and port, taken from the Environment, are ${spring.application.name}, the Spring Context ID and ${server.port} respectively.
Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both a Zookeeper "service" (i.e. it registers itself) and a "client" (i.e. it can query Zookeeper to locate other services).
If you would like to disable the Zookeeper Discovery Client you can set spring.cloud.zookeeper.discovery.enabled to false.
2.3 Using the DiscoveryClient
Spring Cloud has support for Feign (a REST client builder) and also Spring RestTemplate using the logical service names instead of physical URLs.
You can also use the org.springframework.cloud.client.discovery.DiscoveryClient which provides a simple API for discovery clients that is not specific to Netflix, e.g.
@Autowired
+
[Caution]Caution
If you use Spring Cloud Zookeeper Config, the
+values shown in the preceding example need to be in bootstrap.yml instead of
+application.yml.
The default service name, instance ID, and port (taken from the Environment) are
+${spring.application.name}, the Spring Context ID, and ${server.port}, respectively.
Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both
+a Zookeeper “service” (that is, it registers itself) and a “client” (that is, it can
+query Zookeeper to locate other services).
If you would like to disable the Zookeeper Discovery Client, you can set
+spring.cloud.zookeeper.discovery.enabled to false.
2.3 Using the DiscoveryClient
Spring Cloud has support for
+Feign
+(a REST client builder) and
+Spring
+RestTemplate, using logical service names instead of physical URLs.
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, as shown in
+the following example:
@Autowired
 private DiscoveryClient discoveryClient;
 
 public String serviceUrl() {
@@ -33,7 +56,14 @@ Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Brea
         return list.get(0).getUri().toString();
     }
     return null;
-}
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient implementation is used. Feign, Turbine, Ribbon and Zuul all work with Spring Cloud Zookeeper.
3.1 Ribbon with Zookeeper
Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When the spring-cloud-starter-zookeeper-discovery is used, Ribbon is auto-configured to use the ZookeeperServerList by default.
4. Spring Cloud Zookeeper and Service Registry
Spring Cloud Zookeeper implements the ServiceRegistry interface allowing developers to register arbitrary service in a programmatic way.
The ServiceInstanceRegistration class offers a builder() method to create a Registration object that can be used by the ServiceRegistry.
@Autowired
+}
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient
+implementation you use. Feign, Turbine, Ribbon, and Zuul all work with Spring Cloud
+Zookeeper.
3.1 Ribbon with Zookeeper
Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When you use
+the  spring-cloud-starter-zookeeper-discovery, Ribbon is autoconfigured to use the
+ZookeeperServerList by default.
4. Spring Cloud Zookeeper and Service Registry
Spring Cloud Zookeeper implements the ServiceRegistry interface, letting developers
+register arbitrary services in a programmatic way.
The ServiceInstanceRegistration class offers a builder() method to create a
+Registration object that can be used by the ServiceRegistry, as shown in the following
+example:
@Autowired
 private ZookeeperServiceRegistry serviceRegistry;
 
 public void registerThings() {
@@ -44,9 +74,25 @@ Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Brea
             .name("/a/b/c/d/anotherservice")
             .build();
     this.serviceRegistry.register(registration);
-}
4.1 Instance Status
Netflix Eureka supports having instances registered with the server that are OUT_OF_SERVICE and not returned as active service instances. This is very useful for behaviors such as blue/green deployments. The Curator Service Discovery recipe does not support this behavior. Taking advantage of the flexible payload has let Spring Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList filters out all non-null instance statuses that do not equal UP. If the instance status field is empty, it is considered UP for backwards compatibility. To change the status of an instance POST OUT_OF_SERVICE to the ServiceRegistry instance status actuator endpoint.
$ http POST http://localhost:8081/service-registry status=OUT_OF_SERVICE
NOTE: The above example uses the `http` command from https://httpie.org
5. Zookeeper Dependencies
5.1 Using the Zookeeper Dependencies
Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application as properties. As dependencies you can understand other applications that are registered
-in Zookeeper and which you would like to call via Feign (a REST client builder)
-and also Spring RestTemplate.
You can also benefit from the Zookeeper Dependency Watchers functionality that lets you control and monitor what is the state of your dependencies and decide what to do with that.
5.2 How to activate Zookeeper Dependencies
  • Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Dependencies.
  • If you have to have the spring.cloud.zookeeper.dependencies section properly set up - check the subsequent section for more details then the feature is active
  • You can have the dependencies turned off even if you’ve provided the dependencies in your properties. Just set the property spring.cloud.zookeeper.dependency.enabled to false (defaults to true).
5.3 Setting up Zookeeper Dependencies
Let’s take a closer look at an example of dependencies representation:
application.yml. 
+}

4.1 Instance Status

Netflix Eureka supports having instances that are OUT_OF_SERVICE registered with the +server. These instances are not returned as active service instances. This is useful for +behaviors such as blue/green deployments. (Note that the Curator Service Discovery recipe +does not support this behavior.) Taking advantage of the flexible payload has let Spring +Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then +filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList +filters out all non-null instance statuses that do not equal UP. If the instance status +field is empty, it is considered to be UP for backwards compatibility. To change the +status of an instance, make a POST with OUT_OF_SERVICE to the ServiceRegistry +instance status actuator endpoint, as shown in the following example:

$ http POST http://localhost:8081/service-registry status=OUT_OF_SERVICE
[Note]Note

The preceding example uses the http command from https://httpie.org.

5. Zookeeper Dependencies

The following topics cover how to work with Spring Cloud Zookeeper dependencies:

5.1 Using the Zookeeper Dependencies

Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application +as properties. As dependencies, you can understand other applications that are registered +in Zookeeper and which you would like to call through +Feign +(a REST client builder) and Spring RestTemplate.

You can also use the Zookeeper Dependency Watchers functionality to control and monitor +the state of your dependencies.

5.2 Activating Zookeeper Dependencies

Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables +autoconfiguration that sets up Spring Cloud Zookeeper Dependencies. Even if you provide +the dependencies in your properties, you can turn off the dependencies. To do so, set the +spring.cloud.zookeeper.dependency.enabled property to false (it defaults to true).

5.3 Setting up Zookeeper Dependencies

Consider the following example of dependency representation:

application.yml.  

spring.application.name: yourServiceName
 spring.cloud.zookeeper:
   dependencies:
@@ -68,36 +114,94 @@ spring.cloud.zookeeper:
       contentTypeTemplate: application/vnd.mailing.$version+json
       version: v1
       required: true

-

Let’s now go through each part of the dependency one by one. The root property name is spring.cloud.zookeeper.dependencies.

5.3.1 Aliases

Below the root property you have to represent each dependency has by an alias due to the constraints of Ribbon (the application id has to be placed in the URL -thus you can’t pass any complex path like /foo/bar/name). The alias will be the name that you will use instead of serviceId for DiscoveryClient, Feign or RestTemplate.

In the aforementioned examples the aliases are newsletter and mailing. Example of Feign usage with newsletter would be:

@FeignClient("newsletter")
+
The next few sections go through each part of the dependency one by one. The root property
+name is spring.cloud.zookeeper.dependencies.
5.3.1 Aliases
Below the root property you have to represent each dependency as an alias. This is due to
+the constraints of Ribbon, which requires that the application ID be placed in the URL.
+Consequently, you cannot pass any complex path, suchas  /myApp/myRoute/name). The alias
+is the name you use instead of the serviceId for DiscoveryClient, Feign, or
+RestTemplate.
In the previous examples, the aliases are newsletter and mailing. The following
+example shows Feign usage with a newsletter alias:
@FeignClient("newsletter")
 public interface NewsletterService {
         @RequestMapping(method = RequestMethod.GET, value = "/newsletter")
         String getNewsletters();
-}
5.3.2 Path
Represented by path yaml property.
Path is the path under which the dependency is registered under Zookeeper. Like presented before Ribbon operates on URLs thus this path is not compliant with its requirement.
-That is why Spring Cloud Zookeeper maps the alias to the proper path.
5.3.3 Load balancer type
Represented by loadBalancerType yaml property.
If you know what kind of load balancing strategy has to be applied when calling this particular dependency then you can provide it in the yaml file and it will be automatically applied.
-You can choose one of the following load balancing strategies
  • STICKY - once chosen the instance will always be called
  • RANDOM - picks an instance randomly
  • ROUND_ROBIN - iterates over instances over and over again
5.3.4 Content-Type template and version
Represented by contentTypeTemplate and version yaml property.
If you version your api via the Content-Type header then you don’t want to add this header to each of your requests. Also if you want to call a new version of the API you don’t want to
-roam around your code to bump up the API version. That’s why you can provide a contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the
-version yaml property. Let’s take a look at an example.
Having the following contentTypeTemplate:
application/vnd.newsletter.$version+json
and the following version:
v1
Will result in setting up of a Content-Type header for each request:
application/vnd.newsletter.v1+json
5.3.5 Default headers
Represented by headers map in yaml
Sometimes each call to a dependency requires setting up of some default headers. In order not to do that in code you can set them up in the yaml file.
-Having the following headers section:
headers:
+}
5.3.2 Path
The path is represented by the path YAML property and is the path under which the
+dependency is registered under Zookeeper. As described in the
+previous section, Ribbon
+operates on URLs. As a result, this path is not compliant with its requirement.
+That is why Spring Cloud Zookeeper maps the alias to the proper path.
5.3.3 Load Balancer Type
The load balancer type is represented by loadBalancerType YAML property.
If you know what kind of load-balancing strategy has to be applied when calling this
+particular dependency, you can provide it in the YAML file, and it is automatically
+applied. You can choose one of the following load balancing strategies:
  • STICKY: Once chosen, the instance is always called.
  • RANDOM: Picks an instance randomly.
  • ROUND_ROBIN: Iterates over instances over and over again.
5.3.4 Content-Type Template and Version
The Content-Type template and version are represented by the contentTypeTemplate and
+version YAML properties.
If you version your API in the Content-Type header, you do not want to add this header
+to each of your requests. Also, if you want to call a new version of the API, you do not
+want to roam around your code to bump up the API version. That is why you can provide a
+contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the
+version YAML property. Consider the following example of a contentTypeTemplate:
application/vnd.newsletter.$version+json
Further consider the following version:
v1
The combination of contentTypeTemplate and version results in the creation of a
+Content-Type header for each request, as follows:
application/vnd.newsletter.v1+json
5.3.5 Default Headers
Default headers are represented by the headers map in YAML.
Sometimes, each call to a dependency requires setting up of some default headers. To not
+do that in code, you can set them up in the YAML file, as shown in the following example
+headers section:
headers:
     Accept:
         - text/html
         - application/xhtml+xml
     Cache-Control:
-        - no-cache
Results in adding the Accept and Cache-Control headers with appropriate list of values in your HTTP request.
5.3.6 Obligatory dependencies
Represented by required property in yaml
If one of your dependencies is required to be up and running when your application is booting then it’s enough to set up the required: true property in the yaml file.
If your application can’t localize the required dependency during boot time it will throw an exception and the Spring Context will fail to set up.
-In other words your application won’t be able to start if the required dependency is not registered in Zookeeper.
You can read more about Spring Cloud Zookeeper Presence Checker in the following sections.
5.3.7 Stubs
You can provide a colon separated path to the JAR containing stubs of the dependency. Example
stubs: org.springframework:foo:stubs
means that for a particular dependencies can be found under:
  • groupId: org.springframework
  • artifactId: foo
  • classifier: stubs - this is the default value
This is actually equal to
stubs: org.springframework:foo
since stubs is the default classifier.

5.4 Configuring Spring Cloud Zookeeper Dependencies

There is a bunch of properties that you can set to enable / disable parts of Zookeeper Dependencies functionalities.

  • spring.cloud.zookeeper.dependencies - if you don’t set this property you won’t benefit from Zookeeper Dependencies
  • spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default) - Ribbon requires explicit global configuration or a particular one for a dependency. By turning on this property -runtime load balancing strategy resolution is possible and you can profit from the loadBalancerType section of the Zookeeper Dependencies. The configuration that needs this property -has an implementation of LoadBalancerClient that delegates to the ILoadBalancer presented in the next bullet
  • spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default) - thanks to this property the custom ILoadBalancer knows that the part of the URI passed to Ribbon might -actually be the alias that has to be resolved to a proper path in Zookeeper. Without this property you won’t be able to register applications under nested paths.
  • spring.cloud.zookeeper.dependency.headers.enabled (enabled by default) - this property registers such a RibbonClient that automatically will append appropriate headers and content -types with version as presented in the Dependency configuration. Without this setting of those two parameters will not be operational.
  • spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default) - when enabled will modify the request headers of @LoadBalanced annotated RestTemplate so that it passes -headers and content type with version set in Dependency configuration. Wihtout this setting of those two parameters will not be operational.

6. Spring Cloud Zookeeper Dependency Watcher

The Dependency Watcher mechanism allows you to register listeners to your dependencies. The functionality is in fact an implementation of the Observator pattern. When a dependency changes -its state (UP or DOWN) then some custom logic can be applied.

6.1 How to activate

Spring Cloud Zookeeper Dependencies functionality needs to be enabled to profit from Dependency Watcher mechanism.

6.2 Registering a listener

In order to register a listener you have to implement an interface org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and register it as a bean. -The interface gives you one method:

void stateChanged(String dependencyName, DependencyState newState);

If you want to register a listener for a particular dependency then the dependencyName would be the discriminator for your concrete implementation. newState will provide you with information - whether your dependency has changed to CONNECTED or DISCONNECTED.

6.3 Presence Checker

Bound with Dependency Watcher is the functionality called Presence Checker. It allows you to provide custom behaviour upon booting of your application to react accordingly to the state -of your dependencies.

The default implementation of the abstract org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier class is the -org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier which works in the following way.

  • If the dependency is marked us required and it’s not in Zookeeper then upon booting your application will throw an exception and shutdown
  • If dependency is not required the org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker will log that application is missing at WARN level

The functionality can be overridden since the DefaultDependencyPresenceOnStartupVerifier is registered only when there is no bean of DependencyPresenceOnStartupVerifier.

7. Distributed Configuration with Zookeeper

Zookeeper provides a hierarchical namespace that allows clients to store arbitrary data, such as configuration data. Spring Cloud Zookeeper Config is an alternative to the Config Server and Client. Configuration is loaded into the Spring Environment during the special "bootstrap" phase. Configuration is stored in the /config namespace by default. Multiple PropertySource instances are created based on the application’s name and the active profiles that mimicks the Spring Cloud Config order of resolving properties. For example, an application with the name "testApp" and with the "dev" profile will have the following property sources created:

config/testApp,dev
-config/testApp
-config/application,dev
-config/application

The most specific property source is at the top, with the least specific at the bottom. Properties is the config/application namespace are applicable to all applications using zookeeper for configuration. Properties in the config/testApp namespace are only available to the instances of the service named "testApp".

Configuration is currently read on startup of the application. Sending a HTTP POST to /refresh will cause the configuration to be reloaded. Watching the configuration namespace (which Zookeeper supports) is not currently implemented, but will be a future addition to this project.

7.1 How to activate

Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-config will enable auto-configuration that will setup Spring Cloud Zookeeper Config.

7.2 Customizing

Zookeeper Config may be customized using the following properties:

bootstrap.yml.  + - no-cache

That headers section results in adding the Accept and Cache-Control headers with +appropriate list of values in your HTTP request.

5.3.6 Required Dependencies

Required dependencies are represented by required property in YAML.

If one of your dependencies is required to be up when your application boots, you can set +the required: true property in the YAML file.

If your application cannot localize the required dependency during boot time, it throws an +exception, and the Spring Context fails to set up. In other words, your application cannot +start if the required dependency is not registered in Zookeeper.

You can read more about Spring Cloud Zookeeper Presence Checker +later in this document.

5.3.7 Stubs

You can provide a colon-separated path to the JAR containing stubs of the dependency, as +shown in the following example:

stubs: org.springframework:myApp:stubs

where:

  • org.springframework is the groupId.
  • myApp is the artifactId.
  • stubs is the classifier. (Note that stubs is the default value.)

Because stubs is the default classifier, the preceding example is equal to the following +example:

stubs: org.springframework:myApp

5.4 Configuring Spring Cloud Zookeeper Dependencies

You can set the following properties to enable or disable parts of Zookeeper Dependencies +functionalities:

  • spring.cloud.zookeeper.dependencies: If you do not set this property, you cannot use +Zookeeper Dependencies.
  • spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default): Ribbon requires +either explicit global configuration or a particular one for a dependency. By turning on +this property, runtime load balancing strategy resolution is possible, and you can use the +loadBalancerType section of the Zookeeper Dependencies. The configuration that needs +this property has an implementation of LoadBalancerClient that delegates to the +ILoadBalancer presented in the next bullet.
  • spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default): Thanks to +this property, the custom ILoadBalancer knows that the part of the URI passed to Ribbon +might actually be the alias that has to be resolved to a proper path in Zookeeper. Without +this property, you cannot register applications under nested paths.
  • spring.cloud.zookeeper.dependency.headers.enabled (enabled by default): This property +registers a RibbonClient that automatically appends appropriate headers and content +types with their versions, as presented in the Dependency configuration. Without this +setting, those two parameters do not work.
  • spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default): When +enabled, this property modifies the request headers of a @LoadBalanced-annotated +RestTemplate such that it passes headers and content type with the version set in +dependency configuration. Without this setting, those two parameters do not work.

6. Spring Cloud Zookeeper Dependency Watcher

The Dependency Watcher mechanism lets you register listeners to your dependencies. The +functionality is, in fact, an implementation of the Observator pattern. When a +dependency changes, its state (to either UP or DOWN), some custom logic can be applied.

6.1 Activating

Spring Cloud Zookeeper Dependencies functionality needs to be enabled for you to use the +Dependency Watcher mechanism.

6.2 Registering a Listener

To register a listener, you must implement an interface called +org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and +register it as a bean. The interface gives you one method:

void stateChanged(String dependencyName, DependencyState newState);

If you want to register a listener for a particular dependency, the dependencyName would +be the discriminator for your concrete implementation. newState provides you with +information about whether your dependency has changed to CONNECTED or DISCONNECTED.

6.3 Using the Presence Checker

Bound with the Dependency Watcher is the functionality called Presence Checker. It lets +you provide custom behavior when your application boots, to react according to the state +of your dependencies.

The default implementation of the abstract +org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier +class is the +org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier, +which works in the following way.

  1. If the dependency is marked us required and is not in Zookeeper, when your application +boots, it throws an exception and shuts down.
  2. If the dependency is not required, the +org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker +logs that the dependency is missing at the WARN level.

Because the DefaultDependencyPresenceOnStartupVerifier is registered only when there is +no bean of type DependencyPresenceOnStartupVerifier, this functionality can be +overridden.

7. Distributed Configuration with Zookeeper

Zookeeper provides a +hierarchical namespace +that lets clients store arbitrary data, such as configuration data. Spring Cloud Zookeeper +Config is an alternative to the +Config Server and Client. +Configuration is loaded into the Spring Environment during the special “bootstrap” +phase. Configuration is stored in the /config namespace by default. Multiple +PropertySource instances are created, based on the application’s name and the active +profiles, to mimic the Spring Cloud Config order of resolving properties. For example, an +application with a name of testApp and with the dev profile has the following property +sources created for it:

  • config/testApp,dev
  • config/testApp
  • config/application,dev
  • config/application

The most specific property source is at the top, with the least specific at the bottom. +Properties in the config/application namespace apply to all applications that use +zookeeper for configuration. Properties in the config/testApp namespace are available +only to the instances of the service named testApp.

Configuration is currently read on startup of the application. Sending a HTTP POST +request to /refresh causes the configuration to be reloaded. Watching the configuration +namespace (which Zookeeper supports) is not currently implemented.

7.1 Activating

Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-config enables +autoconfiguration that sets up Spring Cloud Zookeeper Config.

7.2 Customizing

Zookeeper Config may be customized by setting the following properties:

bootstrap.yml.  

spring:
   cloud:
     zookeeper:
@@ -106,8 +210,10 @@ config/application

The most specific property source is at the top, with root: configuration defaultContext: apps profileSeparator: '::'

-

  • enabled setting this value to "false" disables Zookeeper Config
  • root sets the base namespace for configuration values
  • defaultContext sets the name used by all applications
  • profileSeparator sets the value of the separator used to separate the profile name in property sources with profiles

7.3 ACLs

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo method of a -CuratorFramework bean. One way to accomplish this is by providing your own CuratorFramework bean:

@BoostrapConfiguration
+
  • enabled: Setting this value to false disables Zookeeper Config.
  • root: Sets the base namespace for configuration values.
  • defaultContext: Sets the name used by all applications.
  • profileSeparator: Sets the value of the separator used to separate the profile name in
+property sources with profiles.

7.3 Access Control Lists (ACLs)

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo +method of a CuratorFramework bean. One way to accomplish this is to provide your own +CuratorFramework bean, as shown in the following example:

@BoostrapConfiguration
 public class CustomCuratorFrameworkConfig {
 
   @Bean
@@ -117,20 +223,21 @@ CuratorFramework bean. One way to accomplish this is by providing your own Curat
     return curator;
   }
 
-}

Consult the ZookeeperAutoConfiguration class -to see how the CuratorFramework bean is configured by default.

Alternatively, you can add your credentials from a class that depends on the existing -CuratorFramework bean:

@BoostrapConfiguration
+}

Consult +the ZookeeperAutoConfiguration class +to see how the CuratorFramework bean’s default configuration.

Alternatively, you can add your credentials from a class that depends on the existing +CuratorFramework bean, as shown in the following example:

@BoostrapConfiguration
 public class DefaultCuratorFrameworkConfig {
 
   public ZookeeperConfig(CuratorFramework curator) {
     curator.addAuthInfo("digest", "user:password".getBytes());
   }
 
-}

This must occur during the boostrapping phase. You can register configuration classes to run -during this phase by annotating them with @BootstrapConfiguration and including them in a -comma-separated list set as the value of the property -org.springframework.cloud.bootstrap.BootstrapConfiguration in the file -resources/META-INF/spring.factories:

resources/META-INF/spring.factories.  +}

The creation of this bean must occur during the boostrapping phase. You can register +configuration classes to run during this phase by annotating them with +@BootstrapConfiguration and including them in a comma-separated list that you set as the +value of the org.springframework.cloud.bootstrap.BootstrapConfiguration property in the +resources/META-INF/spring.factories file, as shown in the following example:

resources/META-INF/spring.factories.  

org.springframework.cloud.bootstrap.BootstrapConfiguration=\
 my.project.CustomCuratorFrameworkConfig,\
 my.project.DefaultCuratorFrameworkConfig

diff --git a/spring-cloud-zookeeper.xml b/spring-cloud-zookeeper.xml index 871a7116..3f57c782 100644 --- a/spring-cloud-zookeeper.xml +++ b/spring-cloud-zookeeper.xml @@ -8,32 +8,42 @@ -This project provides Zookeeper 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 Zookeeper based components. The -patterns provided include Service Discovery and Configuration. -Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Breaker -(Hystrix) are provided by integration with Spring Cloud Netflix. +This project provides Zookeeper integrations for Spring Boot applications through +autoconfiguration and binding to the Spring Environment and other Spring programming model +idioms. With a few annotations, you can quickly enable and configure the common patterns +inside your application and build large distributed systems with Zookeeper based +components. The provided patterns include Service Discovery and Configuration. Integration +with Spring Cloud Netflix provides Intelligent Routing (Zuul), Client Side Load Balancing +(Ribbon), and Circuit Breaker (Hystrix). Install Zookeeper -Please see the installation documentation for instructions on how to install Zookeeper. +See the installation +documentation for instructions on how to install Zookeeper. Service Discovery with Zookeeper -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. Curator(A java library for Zookeeper) provides Service Discovery services via Service Discovery Extension. Spring Cloud Zookeeper leverages this extension for service registration and discovery. -

-How to activate -Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Discovery. +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 difficult to do and can be +brittle. Curator(A Java library for Zookeeper) provides Service +Discovery through a Service Discovery +Extension. Spring Cloud Zookeeper uses this extension for service registration and +discovery. +
+Activating +Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables +autoconfiguration that sets up Spring Cloud Zookeeper Discovery. -You still need to include org.springframework.boot:spring-boot-starter-web for web functionality. +For web functionality, you still need to include +org.springframework.boot:spring-boot-starter-web.
Registering with Zookeeper -When a client registers with Zookeeper, it provides meta-data about itself such as host and port, id and name. -Example Zookeeper client: +When a client registers with Zookeeper, it provides metadata (such as host and port, ID, +and name) about itself. +The following example shows a Zookeeper client: @SpringBootApplication @RestController public class Application { @@ -48,7 +58,11 @@ public class Application { } } -(i.e. utterly normal Spring Boot app). If Zookeeper is located somewhere other than localhost:2181, the configuration is required to locate the server. Example: + +The preceding example is a normal Spring Boot application. + +If Zookeeper is located somewhere other than localhost:2181, the configuration must +provide the location of the server, as shown in the following example: application.yml @@ -59,16 +73,28 @@ public class Application { -If you use Spring Cloud Zookeeper Config, the above values will need to be placed in bootstrap.yml instead of application.yml. +If you use Spring Cloud Zookeeper Config, the +values shown in the preceding example need to be in bootstrap.yml instead of +application.yml. -The default service name, instance id and port, taken from the Environment, are ${spring.application.name}, the Spring Context ID and ${server.port} respectively. -Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both a Zookeeper "service" (i.e. it registers itself) and a "client" (i.e. it can query Zookeeper to locate other services). -If you would like to disable the Zookeeper Discovery Client you can set spring.cloud.zookeeper.discovery.enabled to false. +The default service name, instance ID, and port (taken from the Environment) are +${spring.application.name}, the Spring Context ID, and ${server.port}, respectively. +Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both +a Zookeeper “service” (that is, it registers itself) and a “client” (that is, it can +query Zookeeper to locate other services). +If you would like to disable the Zookeeper Discovery Client, you can set +spring.cloud.zookeeper.discovery.enabled to false.
Using the DiscoveryClient -Spring Cloud has support for Feign (a REST client builder) and also Spring RestTemplate using the logical service names instead of physical URLs. -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. +Spring Cloud has support for +Feign +(a REST client builder) and +Spring +RestTemplate, using logical service names instead of physical URLs. +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, as shown in +the following example: @Autowired private DiscoveryClient discoveryClient; @@ -83,16 +109,23 @@ public String serviceUrl() { Using Spring Cloud Zookeeper with Spring Cloud Netflix Components -Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient implementation is used. Feign, Turbine, Ribbon and Zuul all work with Spring Cloud Zookeeper. +Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient +implementation you use. Feign, Turbine, Ribbon, and Zuul all work with Spring Cloud +Zookeeper.
Ribbon with Zookeeper -Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When the spring-cloud-starter-zookeeper-discovery is used, Ribbon is auto-configured to use the ZookeeperServerList by default. +Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When you use +the spring-cloud-starter-zookeeper-discovery, Ribbon is autoconfigured to use the +ZookeeperServerList by default.
Spring Cloud Zookeeper and Service Registry -Spring Cloud Zookeeper implements the ServiceRegistry interface allowing developers to register arbitrary service in a programmatic way. -The ServiceInstanceRegistration class offers a builder() method to create a Registration object that can be used by the ServiceRegistry. +Spring Cloud Zookeeper implements the ServiceRegistry interface, letting developers +register arbitrary services in a programmatic way. +The ServiceInstanceRegistration class offers a builder() method to create a +Registration object that can be used by the ServiceRegistry, as shown in the following +example: @Autowired private ZookeeperServiceRegistry serviceRegistry; @@ -107,37 +140,60 @@ public void registerThings() { }
Instance Status -Netflix Eureka supports having instances registered with the server that are OUT_OF_SERVICE and not returned as active service instances. This is very useful for behaviors such as blue/green deployments. The Curator Service Discovery recipe does not support this behavior. Taking advantage of the flexible payload has let Spring Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList filters out all non-null instance statuses that do not equal UP. If the instance status field is empty, it is considered UP for backwards compatibility. To change the status of an instance POST OUT_OF_SERVICE to the ServiceRegistry instance status actuator endpoint. +Netflix Eureka supports having instances that are OUT_OF_SERVICE registered with the +server. These instances are not returned as active service instances. This is useful for +behaviors such as blue/green deployments. (Note that the Curator Service Discovery recipe +does not support this behavior.) Taking advantage of the flexible payload has let Spring +Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then +filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList +filters out all non-null instance statuses that do not equal UP. If the instance status +field is empty, it is considered to be UP for backwards compatibility. To change the +status of an instance, make a POST with OUT_OF_SERVICE to the ServiceRegistry +instance status actuator endpoint, as shown in the following example: $ http POST http://localhost:8081/service-registry status=OUT_OF_SERVICE -NOTE: The above example uses the `http` command from https://httpie.org + +The preceding example uses the http command from https://httpie.org. +
Zookeeper Dependencies -
-Using the Zookeeper Dependencies -Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application as properties. As dependencies you can understand other applications that are registered -in Zookeeper and which you would like to call via Feign (a REST client builder) -and also Spring RestTemplate. -You can also benefit from the Zookeeper Dependency Watchers functionality that lets you control and monitor what is the state of your dependencies and decide what to do with that. -
-
-How to activate Zookeeper Dependencies +The following topics cover how to work with Spring Cloud Zookeeper dependencies: -Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Dependencies. + -If you have to have the spring.cloud.zookeeper.dependencies section properly set up - check the subsequent section for more details then the feature is active + -You can have the dependencies turned off even if you’ve provided the dependencies in your properties. Just set the property spring.cloud.zookeeper.dependency.enabled to false (defaults to true). + + + + +
+Using the Zookeeper Dependencies +Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application +as properties. As dependencies, you can understand other applications that are registered +in Zookeeper and which you would like to call through +Feign +(a REST client builder) and Spring RestTemplate. +You can also use the Zookeeper Dependency Watchers functionality to control and monitor +the state of your dependencies.
-
+
+Activating Zookeeper Dependencies +Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-discovery enables +autoconfiguration that sets up Spring Cloud Zookeeper Dependencies. Even if you provide +the dependencies in your properties, you can turn off the dependencies. To do so, set the +spring.cloud.zookeeper.dependency.enabled property to false (it defaults to true). +
+
Setting up Zookeeper Dependencies -Let’s take a closer look at an example of dependencies representation: +Consider the following example of dependency representation: application.yml @@ -164,12 +220,17 @@ spring.cloud.zookeeper: required: true -Let’s now go through each part of the dependency one by one. The root property name is spring.cloud.zookeeper.dependencies. -
+The next few sections go through each part of the dependency one by one. The root property +name is spring.cloud.zookeeper.dependencies. +
Aliases -Below the root property you have to represent each dependency has by an alias due to the constraints of Ribbon (the application id has to be placed in the URL -thus you can’t pass any complex path like /foo/bar/name). The alias will be the name that you will use instead of serviceId for DiscoveryClient, Feign or RestTemplate. -In the aforementioned examples the aliases are newsletter and mailing. Example of Feign usage with newsletter would be: +Below the root property you have to represent each dependency as an alias. This is due to +the constraints of Ribbon, which requires that the application ID be placed in the URL. +Consequently, you cannot pass any complex path, suchas /myApp/myRoute/name). The alias +is the name you use instead of the serviceId for DiscoveryClient, Feign, or +RestTemplate. +In the previous examples, the aliases are newsletter and mailing. The following +example shows Feign usage with a newsletter alias: @FeignClient("newsletter") public interface NewsletterService { @RequestMapping(method = RequestMethod.GET, value = "/newsletter") @@ -178,158 +239,221 @@ public interface NewsletterService {
Path -Represented by path yaml property. -Path is the path under which the dependency is registered under Zookeeper. Like presented before Ribbon operates on URLs thus this path is not compliant with its requirement. +The path is represented by the path YAML property and is the path under which the +dependency is registered under Zookeeper. As described in the +previous section, Ribbon +operates on URLs. As a result, this path is not compliant with its requirement. That is why Spring Cloud Zookeeper maps the alias to the proper path.
-Load balancer type -Represented by loadBalancerType yaml property. -If you know what kind of load balancing strategy has to be applied when calling this particular dependency then you can provide it in the yaml file and it will be automatically applied. -You can choose one of the following load balancing strategies +Load Balancer Type +The load balancer type is represented by loadBalancerType YAML property. +If you know what kind of load-balancing strategy has to be applied when calling this +particular dependency, you can provide it in the YAML file, and it is automatically +applied. You can choose one of the following load balancing strategies: -STICKY - once chosen the instance will always be called +STICKY: Once chosen, the instance is always called. -RANDOM - picks an instance randomly +RANDOM: Picks an instance randomly. -ROUND_ROBIN - iterates over instances over and over again +ROUND_ROBIN: Iterates over instances over and over again.
-
-Content-Type template and version -Represented by contentTypeTemplate and version yaml property. -If you version your api via the Content-Type header then you don’t want to add this header to each of your requests. Also if you want to call a new version of the API you don’t want to -roam around your code to bump up the API version. That’s why you can provide a contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the -version yaml property. Let’s take a look at an example. -Having the following contentTypeTemplate: +
+<literal>Content-Type</literal> Template and Version +The Content-Type template and version are represented by the contentTypeTemplate and +version YAML properties. +If you version your API in the Content-Type header, you do not want to add this header +to each of your requests. Also, if you want to call a new version of the API, you do not +want to roam around your code to bump up the API version. That is why you can provide a +contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the +version YAML property. Consider the following example of a contentTypeTemplate: application/vnd.newsletter.$version+json -and the following version: +Further consider the following version: v1 -Will result in setting up of a Content-Type header for each request: +The combination of contentTypeTemplate and version results in the creation of a +Content-Type header for each request, as follows: application/vnd.newsletter.v1+json
-Default headers -Represented by headers map in yaml -Sometimes each call to a dependency requires setting up of some default headers. In order not to do that in code you can set them up in the yaml file. -Having the following headers section: +Default Headers +Default headers are represented by the headers map in YAML. +Sometimes, each call to a dependency requires setting up of some default headers. To not +do that in code, you can set them up in the YAML file, as shown in the following example +headers section: headers: Accept: - text/html - application/xhtml+xml Cache-Control: - no-cache -Results in adding the Accept and Cache-Control headers with appropriate list of values in your HTTP request. +That headers section results in adding the Accept and Cache-Control headers with +appropriate list of values in your HTTP request.
-
-Obligatory dependencies -Represented by required property in yaml -If one of your dependencies is required to be up and running when your application is booting then it’s enough to set up the required: true property in the yaml file. -If your application can’t localize the required dependency during boot time it will throw an exception and the Spring Context will fail to set up. -In other words your application won’t be able to start if the required dependency is not registered in Zookeeper. -You can read more about Spring Cloud Zookeeper Presence Checker in the following sections. +
+Required Dependencies +Required dependencies are represented by required property in YAML. +If one of your dependencies is required to be up when your application boots, you can set +the required: true property in the YAML file. +If your application cannot localize the required dependency during boot time, it throws an +exception, and the Spring Context fails to set up. In other words, your application cannot +start if the required dependency is not registered in Zookeeper. +You can read more about Spring Cloud Zookeeper Presence Checker +later in this document.
Stubs -You can provide a colon separated path to the JAR containing stubs of the dependency. Example -stubs: org.springframework:foo:stubs -means that for a particular dependencies can be found under: +You can provide a colon-separated path to the JAR containing stubs of the dependency, as +shown in the following example: +stubs: org.springframework:myApp:stubs +where: -groupId: org.springframework +org.springframework is the groupId. -artifactId: foo +myApp is the artifactId. -classifier: stubs - this is the default value +stubs is the classifier. (Note that stubs is the default value.) -This is actually equal to -stubs: org.springframework:foo -since stubs is the default classifier. +Because stubs is the default classifier, the preceding example is equal to the following +example: +stubs: org.springframework:myApp
-
+
Configuring Spring Cloud Zookeeper Dependencies -There is a bunch of properties that you can set to enable / disable parts of Zookeeper Dependencies functionalities. +You can set the following properties to enable or disable parts of Zookeeper Dependencies +functionalities: -spring.cloud.zookeeper.dependencies - if you don’t set this property you won’t benefit from Zookeeper Dependencies +spring.cloud.zookeeper.dependencies: If you do not set this property, you cannot use +Zookeeper Dependencies. -spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default) - Ribbon requires explicit global configuration or a particular one for a dependency. By turning on this property -runtime load balancing strategy resolution is possible and you can profit from the loadBalancerType section of the Zookeeper Dependencies. The configuration that needs this property -has an implementation of LoadBalancerClient that delegates to the ILoadBalancer presented in the next bullet +spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default): Ribbon requires +either explicit global configuration or a particular one for a dependency. By turning on +this property, runtime load balancing strategy resolution is possible, and you can use the +loadBalancerType section of the Zookeeper Dependencies. The configuration that needs +this property has an implementation of LoadBalancerClient that delegates to the +ILoadBalancer presented in the next bullet. -spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default) - thanks to this property the custom ILoadBalancer knows that the part of the URI passed to Ribbon might -actually be the alias that has to be resolved to a proper path in Zookeeper. Without this property you won’t be able to register applications under nested paths. +spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default): Thanks to +this property, the custom ILoadBalancer knows that the part of the URI passed to Ribbon +might actually be the alias that has to be resolved to a proper path in Zookeeper. Without +this property, you cannot register applications under nested paths. -spring.cloud.zookeeper.dependency.headers.enabled (enabled by default) - this property registers such a RibbonClient that automatically will append appropriate headers and content -types with version as presented in the Dependency configuration. Without this setting of those two parameters will not be operational. +spring.cloud.zookeeper.dependency.headers.enabled (enabled by default): This property +registers a RibbonClient that automatically appends appropriate headers and content +types with their versions, as presented in the Dependency configuration. Without this +setting, those two parameters do not work. -spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default) - when enabled will modify the request headers of @LoadBalanced annotated RestTemplate so that it passes -headers and content type with version set in Dependency configuration. Wihtout this setting of those two parameters will not be operational. +spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default): When +enabled, this property modifies the request headers of a @LoadBalanced-annotated +RestTemplate such that it passes headers and content type with the version set in +dependency configuration. Without this setting, those two parameters do not work.
Spring Cloud Zookeeper Dependency Watcher -The Dependency Watcher mechanism allows you to register listeners to your dependencies. The functionality is in fact an implementation of the Observator pattern. When a dependency changes -its state (UP or DOWN) then some custom logic can be applied. -
-How to activate -Spring Cloud Zookeeper Dependencies functionality needs to be enabled to profit from Dependency Watcher mechanism. +The Dependency Watcher mechanism lets you register listeners to your dependencies. The +functionality is, in fact, an implementation of the Observator pattern. When a +dependency changes, its state (to either UP or DOWN), some custom logic can be applied. +
+Activating +Spring Cloud Zookeeper Dependencies functionality needs to be enabled for you to use the +Dependency Watcher mechanism.
-Registering a listener -In order to register a listener you have to implement an interface org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and register it as a bean. -The interface gives you one method: +Registering a Listener +To register a listener, you must implement an interface called +org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and +register it as a bean. The interface gives you one method: void stateChanged(String dependencyName, DependencyState newState); -If you want to register a listener for a particular dependency then the dependencyName would be the discriminator for your concrete implementation. newState will provide you with information - whether your dependency has changed to CONNECTED or DISCONNECTED. +If you want to register a listener for a particular dependency, the dependencyName would +be the discriminator for your concrete implementation. newState provides you with +information about whether your dependency has changed to CONNECTED or DISCONNECTED.
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-Presence Checker -Bound with Dependency Watcher is the functionality called Presence Checker. It allows you to provide custom behaviour upon booting of your application to react accordingly to the state +
+Using the Presence Checker +Bound with the Dependency Watcher is the functionality called Presence Checker. It lets +you provide custom behavior when your application boots, to react according to the state of your dependencies. -The default implementation of the abstract org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier class is the -org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier which works in the following way. - +The default implementation of the abstract +org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier +class is the +org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier, +which works in the following way. + -If the dependency is marked us required and it’s not in Zookeeper then upon booting your application will throw an exception and shutdown +If the dependency is marked us required and is not in Zookeeper, when your application +boots, it throws an exception and shuts down. -If dependency is not required the org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker will log that application is missing at WARN level +If the dependency is not required, the +org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker +logs that the dependency is missing at the WARN level. - -The functionality can be overridden since the DefaultDependencyPresenceOnStartupVerifier is registered only when there is no bean of DependencyPresenceOnStartupVerifier. + +Because the DefaultDependencyPresenceOnStartupVerifier is registered only when there is +no bean of type DependencyPresenceOnStartupVerifier, this functionality can be +overridden.
Distributed Configuration with Zookeeper -Zookeeper provides a hierarchical namespace that allows clients to store arbitrary data, such as configuration data. Spring Cloud Zookeeper Config is an alternative to the Config Server and Client. Configuration is loaded into the Spring Environment during the special "bootstrap" phase. Configuration is stored in the /config namespace by default. Multiple PropertySource instances are created based on the application’s name and the active profiles that mimicks the Spring Cloud Config order of resolving properties. For example, an application with the name "testApp" and with the "dev" profile will have the following property sources created: -config/testApp,dev -config/testApp -config/application,dev -config/application -The most specific property source is at the top, with the least specific at the bottom. Properties is the config/application namespace are applicable to all applications using zookeeper for configuration. Properties in the config/testApp namespace are only available to the instances of the service named "testApp". -Configuration is currently read on startup of the application. Sending a HTTP POST to /refresh will cause the configuration to be reloaded. Watching the configuration namespace (which Zookeeper supports) is not currently implemented, but will be a future addition to this project. -
-How to activate -Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-config will enable auto-configuration that will setup Spring Cloud Zookeeper Config. +Zookeeper provides a +hierarchical namespace +that lets clients store arbitrary data, such as configuration data. Spring Cloud Zookeeper +Config is an alternative to the +Config Server and Client. +Configuration is loaded into the Spring Environment during the special “bootstrap” +phase. Configuration is stored in the /config namespace by default. Multiple +PropertySource instances are created, based on the application’s name and the active +profiles, to mimic the Spring Cloud Config order of resolving properties. For example, an +application with a name of testApp and with the dev profile has the following property +sources created for it: + + +config/testApp,dev + + +config/testApp + + +config/application,dev + + +config/application + + +The most specific property source is at the top, with the least specific at the bottom. +Properties in the config/application namespace apply to all applications that use +zookeeper for configuration. Properties in the config/testApp namespace are available +only to the instances of the service named testApp. +Configuration is currently read on startup of the application. Sending a HTTP POST +request to /refresh causes the configuration to be reloaded. Watching the configuration +namespace (which Zookeeper supports) is not currently implemented. +
+Activating +Including a dependency on +org.springframework.cloud:spring-cloud-starter-zookeeper-config enables +autoconfiguration that sets up Spring Cloud Zookeeper Config.
Customizing -Zookeeper Config may be customized using the following properties: +Zookeeper Config may be customized by setting the following properties: bootstrap.yml @@ -345,23 +469,25 @@ config/application -enabled setting this value to "false" disables Zookeeper Config +enabled: Setting this value to false disables Zookeeper Config. -root sets the base namespace for configuration values +root: Sets the base namespace for configuration values. -defaultContext sets the name used by all applications +defaultContext: Sets the name used by all applications. -profileSeparator sets the value of the separator used to separate the profile name in property sources with profiles +profileSeparator: Sets the value of the separator used to separate the profile name in +property sources with profiles.
-
-ACLs -You can add authentication information for Zookeeper ACLs by calling the addAuthInfo method of a -CuratorFramework bean. One way to accomplish this is by providing your own CuratorFramework bean: +
+Access Control Lists (ACLs) +You can add authentication information for Zookeeper ACLs by calling the addAuthInfo +method of a CuratorFramework bean. One way to accomplish this is to provide your own +CuratorFramework bean, as shown in the following example: @BoostrapConfiguration public class CustomCuratorFrameworkConfig { @@ -373,10 +499,11 @@ public class CustomCuratorFrameworkConfig { } } -Consult the ZookeeperAutoConfiguration class -to see how the CuratorFramework bean is configured by default. +Consult +the ZookeeperAutoConfiguration class +to see how the CuratorFramework bean’s default configuration. Alternatively, you can add your credentials from a class that depends on the existing -CuratorFramework bean: +CuratorFramework bean, as shown in the following example: @BoostrapConfiguration public class DefaultCuratorFrameworkConfig { @@ -385,11 +512,11 @@ public class DefaultCuratorFrameworkConfig { } } -This must occur during the boostrapping phase. You can register configuration classes to run -during this phase by annotating them with @BootstrapConfiguration and including them in a -comma-separated list set as the value of the property -org.springframework.cloud.bootstrap.BootstrapConfiguration in the file -resources/META-INF/spring.factories: +The creation of this bean must occur during the boostrapping phase. You can register +configuration classes to run during this phase by annotating them with +@BootstrapConfiguration and including them in a comma-separated list that you set as the +value of the org.springframework.cloud.bootstrap.BootstrapConfiguration property in the +resources/META-INF/spring.factories file, as shown in the following example: resources/META-INF/spring.factories