2. Spring Cloud Commons: Common Abstractions
Patterns such as service discovery, load balancing and circuit breakers lend themselves to a common abstraction layer that can be consumed by all Spring Cloud clients, independent of the implementation (e.g. discovery via Eureka or Consul).
2.1 @EnableDiscoveryClient
Commons provides the @EnableDiscoveryClient annotation. This looks for implementations of the DiscoveryClient interface via META-INF/spring.factories. Implementations of Discovery Client will add a configuration class to spring.factories under the org.springframework.cloud.client.discovery.EnableDiscoveryClient key. Examples of DiscoveryClient implementations: are Spring Cloud Netflix Eureka, Spring Cloud Consul Discovery and Spring Cloud Zookeeper Discovery.
By default, implementations of DiscoveryClient will auto-register the local Spring Boot server with the remote discovery server. This can be disabled by setting autoRegister=false in @EnableDiscoveryClient.
![[Note]](images/note.png) | Note |
|---|
The use of @EnableDiscoveryClient is no longer required. It is enough to just have a DiscoveryClient implementation
-on the classpath to cause the Spring Boot application to register with the service discovery server. |
Commons creates a Spring Boot HealthIndicator that DiscoveryClient implementations can participate in by implementing DiscoveryHealthIndicator. To disable the composite HealthIndicator set spring.cloud.discovery.client.composite-indicator.enabled=false. A generic HealthIndicator based on DiscoveryClient is auto-configured (DiscoveryClientHealthIndicator). To disable it, set `spring.cloud.discovery.client.health-indicator.enabled=false. To disable the description field of the DiscoveryClientHealthIndicator set spring.cloud.discovery.client.health-indicator.include-description=false, otherwise it can bubble up as the description of the rolled up HealthIndicator.
Commons now provides a ServiceRegistry interface which provides methods like register(Registration) and deregister(Registration) which allow you to provide custom registered services. Registration is a marker interface.
@Configuration
+on the classpath to cause the Spring Boot application to register with the service discovery server.
Commons creates a Spring Boot HealthIndicator that DiscoveryClient implementations can participate in by implementing DiscoveryHealthIndicator. To disable the composite HealthIndicator set spring.cloud.discovery.client.composite-indicator.enabled=false. A generic HealthIndicator based on DiscoveryClient is auto-configured (DiscoveryClientHealthIndicator). To disable it, set spring.cloud.discovery.client.health-indicator.enabled=false. To disable the description field of the DiscoveryClientHealthIndicator set spring.cloud.discovery.client.health-indicator.include-description=false, otherwise it can bubble up as the description of the rolled up HealthIndicator.
Commons now provides a ServiceRegistry interface which provides methods like register(Registration) and deregister(Registration) which allow you to provide custom registered services. Registration is a marker interface.
@Configuration
@EnableDiscoveryClient(autoRegister=false)
public class MyConfiguration {
private ServiceRegistry registry;
@@ -15,7 +15,7 @@ on the classpath to cause the Spring Boot application to register with the servi
Registration registration = constructRegistration();
this.registry.register(registration);
}
-}Each ServiceRegistry implementation has its own Registry implementation.
2.2.1 ServiceRegistry Auto-Registration
By default, the ServiceRegistry implementation will auto-register the running service. To disable that behavior, there are two methods. You can set @EnableDiscoveryClient(autoRegister=false) to permanently disable auto-registration. You can also set spring.cloud.service-registry.auto-registration.enabled=false to disable the behavior via configuration.
2.2.2 Service Registry Actuator Endpoint
A /service-registry actuator endpoint is provided by Commons. This endpoint relys on a Registration bean in the Spring Application Context. Calling /service-registry/instance-status via a GET will return the status of the Registration. A POST to the same endpoint with a String body will change the status of the current Registration to the new value. Please see the documentation of the ServiceRegistry implementation you are using for the allowed values for updating the status and the values retured for the status.
2.3 Spring RestTemplate as a Load Balancer Client
RestTemplate can be automatically configured to use ribbon. To create a load balanced RestTemplate create a RestTemplate @Bean and use the @LoadBalanced qualifier.
![[Warning]](images/warning.png) | Warning |
|---|
A RestTemplate bean is no longer created via auto configuration. It must be created by individual applications. |
@Configuration
+}
Each ServiceRegistry implementation has its own Registry implementation.
2.2.1 ServiceRegistry Auto-Registration
By default, the ServiceRegistry implementation will auto-register the running service. To disable that behavior, there are two methods. You can set @EnableDiscoveryClient(autoRegister=false) to permanently disable auto-registration. You can also set spring.cloud.service-registry.auto-registration.enabled=false to disable the behavior via configuration.
2.2.2 Service Registry Actuator Endpoint
A /service-registry actuator endpoint is provided by Commons. This endpoint relies on a Registration bean in the Spring Application Context. Calling /service-registry via a GET will return the status of the Registration. A POST to the same endpoint with a JSON body will change the status of the current Registration to the new value. The JSON body has to include the status field with the preferred value. Please see the documentation of the ServiceRegistry implementation you are using for the allowed values for updating the status and the values returned for the status. For instance, Eureka’s supported statuses are UP, DOWN, OUT_OF_SERVICE and UNKNOWN.
2.3 Spring RestTemplate as a Load Balancer Client
RestTemplate can be automatically configured to use ribbon. To create a load balanced RestTemplate create a RestTemplate @Bean and use the @LoadBalanced qualifier.
| Warning |
|---|
A RestTemplate bean is no longer created via auto configuration. It must be created by individual applications. |
@Configuration
public class MyConfiguration {
@LoadBalanced
@@ -182,4 +182,23 @@ in downstream projects. In addition, if you provide a bean of type spring.cloud.httpclientfactories.apache.enabled or spring.cloud.httpclientfactories.ok.enabled to
-false.A /features actuator endpoint is provided by Commons. This endpoint returns features available on the classpath and if they are enabled or not. The information returned includes the feature type, name, version and vendor.
There are two types of 'features': abstract and named.
Abstract features are features where an interface or abstract class is defined that an implementation creates, such as DiscoveryClient, LoadBalancerClient or LockService. The abstract class or interface is used to find a bean of that type in the context. The version displayed is bean.getClass().getPackage().getImplementationVersion().
Named features are features that don’t have a particular class they implement, such as "Circuit Breaker", "API Gateway", "Spring Cloud Bus", etc… These features require a name and a bean type.
Any module can declare any number of HasFeature beans. Some examples:
@Bean
+public HasFeatures commonsFeatures() {
+ return HasFeatures.abstractFeatures(DiscoveryClient.class, LoadBalancerClient.class);
+}
+
+@Bean
+public HasFeatures consulFeatures() {
+ return HasFeatures.namedFeatures(
+ new NamedFeature("Spring Cloud Bus", ConsulBusAutoConfiguration.class),
+ new NamedFeature("Circuit Breaker", HystrixCommandAspect.class));
+}
+
+@Bean
+HasFeatures localFeatures() {
+ return HasFeatures.builder()
+ .abstractFeature(Foo.class)
+ .namedFeature(new NamedFeature("Bar Feature", Bar.class))
+ .abstractFeature(Baz.class)
+ .build();
+}Each of these beans should go in an appropriately guarded @Configuration.