2. Service Discovery with Zookeeper

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

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

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

Example Zookeeper client:

@SpringBootApplication
@RestController
public class Application {

    @RequestMapping("/")
    public String home() {
        return "Hello world";
    }

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);
    }

}

(i.e. utterly normal Spring Boot app). If Zookeeper is located somewhere other than localhost:2181, the configuration is required to locate the server. Example:

application.yml. 

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

	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.

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
private DiscoveryClient discoveryClient;

public String serviceUrl() {
    List<ServiceInstance> list = discoveryClient.getInstances("STORES");
    if (list != null && list.size() > 0 ) {
        return list.get(0).getUri().toString();
    }
    return null;
}