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).

@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.

ServiceRegistry

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;

    public MyConfiguration(ServiceRegistry registry) {
        this.registry = registry;
    }

    // called via some external process, such as an event or a custom actuator endpoint
    public void register() {
        Registration registration = constructRegistration();
        this.registry.register(registration);
    }
}

Each ServiceRegistry implementation has its own Registry implementation.

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.

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.

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.

@Configuration
public class MyConfiguration {

    @LoadBalanced
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

public class MyClass {
    @Autowired
    private RestTemplate restTemplate;

    public String doOtherStuff() {
        String results = restTemplate.getForObject("http://stores/stores", String.class);
        return results;
    }
}

The URI needs to use a virtual host name (ie. service name, not a host name). The Ribbon client is used to create a full physical address. See RibbonAutoConfiguration for details of how the RestTemplate is set up.

Retrying Failed Requests

A load balanced RestTemplate can be configured to retry failed requests. By default this logic is disabled, you can enable it by adding Spring Retry to your application’s classpath. The load balanced RestTemplate will honor some of the Ribbon configuration values related to retrying failed requests. If you would like to disable the retry logic with Spring Retry on the classpath you can set spring.cloud.loadbalancer.retry.enabled=false. The properties you can use are client.ribbon.MaxAutoRetries, client.ribbon.MaxAutoRetriesNextServer, and client.ribbon.OkToRetryOnAllOperations. See the Ribbon documentation for a description of what there properties do.

Multiple RestTemplate objects

If you want a RestTemplate that is not load balanced, create a RestTemplate bean and inject it as normal. To access the load balanced RestTemplate use the @LoadBalanced qualifier when you create your @Bean.

@Configuration
public class MyConfiguration {

    @LoadBalanced
    @Bean
    RestTemplate loadBalanced() {
        return new RestTemplate();
    }

    @Primary
    @Bean
    RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

public class MyClass {
    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    @LoadBalanced
    private RestTemplate loadBalanced;

    public String doOtherStuff() {
        return loadBalanced.getForObject("http://stores/stores", String.class);
    }

    public String doStuff() {
        return restTemplate.getForObject("http://example.com", String.class);
    }
}

Ignore Network Interfaces

Sometimes it is useful to ignore certain named network interfaces so they can be excluded from Service Discovery registration (eg. running in a Docker container). A list of regular expressions can be set that will cause the desired network interfaces to be ignored. The following configuration will ignore the "docker0" interface and all interfaces that start with "veth".

application.yml

spring:
  cloud:
    inetutils:
      ignoredInterfaces:
        - docker0
        - veth.*

You can also force to use only specified network addresses using list of regular expressions:

application.yml

spring:
  cloud:
    inetutils:
      preferredNetworks:
        - 192.168
        - 10.0

You can also force to use only site local addresses. See Inet4Address.html.isSiteLocalAddress() for more details what is site local address.

application.yml

spring:
  cloud:
    inetutils:
      useOnlySiteLocalInterfaces: true