Eureka service discovery without Spring-boot

Question

I have written a spring boot micro-service and a REST client. The client is a part of another module and make RESTful calls to the micro-service. The micro-service registers with the Eureka registry and I want my client (Which is not a spring boot project) to use the Eureka to query and get the service endpoints.

My problem is since the client is not a Spring-Boot applications I can not use the annotations like @SpringBootApplication, @EnableDiscoveryClient and the DiscoveryClient is not get auto wired to the application. Is there anyway to manually auto-wire the DiscoveryClient bean to the client without using the annotations ?

Answer 1

Well this is how I did It. Basically it is a lot easier than I anticipated. The following was copied from Netflix eureka project.

  DiscoveryManager.getInstance().initComponent(new MyDataCenterInstanceConfig(), new DefaultEurekaClientConfig());

  String vipAddress = "MY-SERVICE";

    InstanceInfo nextServerInfo = null;
    try {
        nextServerInfo = DiscoveryManager.getInstance()
                .getEurekaClient()
                .getNextServerFromEureka(vipAddress, false);
    } catch (Exception e) {
        System.err.println("Cannot get an instance of example service to talk to from eureka");
        System.exit(-1);
    }

    System.out.println("Found an instance of example service to talk to from eureka: "
            + nextServerInfo.getVIPAddress() + ":" + nextServerInfo.getPort());

    System.out.println("healthCheckUrl: " + nextServerInfo.getHealthCheckUrl());
    System.out.println("override: " + nextServerInfo.getOverriddenStatus());

    System.out.println("Server Host Name "+ nextServerInfo.getHostName() + " at port " + nextServerInfo.getPort() );

Also you have to add a configuration file to the class path. Eureka client uses this file to read the information about the eureka servers.

eureka.preferSameZone=true
eureka.shouldUseDns=false
eureka.serviceUrl.default=http://localhost:8761/eureka/
eureka.decoderName=JacksonJson

Also you have to provide the eureka client as a dependency. Eureka1 supports JDK7 though some part of it has been built with JDK8. However I had to provide older versions of "archaius-core" and "servo-core" to make it run with JDK7.

    <dependency>
        <groupId>com.netflix.archaius</groupId>
        <artifactId>archaius-core</artifactId>
        <version>0.7.3</version>
    </dependency>
    <dependency>
        <groupId>com.netflix.servo</groupId>
        <artifactId>servo-core</artifactId>
        <version>0.10.0</version>
    </dependency>

Eureka2 fully supports JDK7.

Answer 2

Either you use the netflix-eureka-client without spring-cloud and have to configure all by yourself (which means duplicating EurekaDiscoveryClientConfiguration)

Or you could run a sidecar service. The sidecar includes a zuul-proxy which would proxy the services discovered by eureka. Have a look int the Spring Cloud Docs - Polyglot support with Sidecar

Answer 3

Wish accessing Eureka from legacy spring ( non-boot ) is also made simple like @EnableEureka and @EnableFeignClient

This is the closest I could get it working . This example is available in Eureka-examples in Git Hub

public class EurekaConfiguration {

    private static ApplicationInfoManager applicationInfoManager;
    private static EurekaClient eurekaClient;

    private static synchronized ApplicationInfoManager initializeApplicationInfoManager(
            EurekaInstanceConfig instanceConfig) {
        if (applicationInfoManager == null) {
            InstanceInfo instanceInfo = new EurekaConfigBasedInstanceInfoProvider(instanceConfig).get();
            applicationInfoManager = new ApplicationInfoManager(instanceConfig, instanceInfo);
        }

        return applicationInfoManager;
    }

    private static synchronized EurekaClient initializeEurekaClient(ApplicationInfoManager applicationInfoManager,
            EurekaClientConfig clientConfig) {
        if (eurekaClient == null) {
            eurekaClient = new DiscoveryClient(applicationInfoManager, clientConfig);
        }

        return eurekaClient;
    }

    public static EurekaClient getEurekaClient()
    {
        ApplicationInfoManager applicationInfoManager = initializeApplicationInfoManager(new MyDataCenterInstanceConfig());
        EurekaClient client = initializeEurekaClient(applicationInfoManager, new DefaultEurekaClientConfig());
        return eurekaClient;
    }
}

My client

String vipAddress = "NLPService";

        InstanceInfo nextServerInfo = null;
        try {
            nextServerInfo = EurekaConfiguration.getEurekaClient().getNextServerFromEureka(vipAddress, false);
        } catch (Exception e) {
            System.err.println("Cannot get an instance of example service to talk to from eureka");
            System.exit(-1);
        }

        System.out.println("Found an instance of example service to talk to from eureka: "
                + nextServerInfo.getVIPAddress() + ":" + nextServerInfo.getPort());

        String serviceBaseURL = "http://"+ nextServerInfo.getHostName()
        +":"+nextServerInfo.getPort();


        String nlpServiceURL = serviceBaseURL +"/nlp";

        RestTemplate restTemplate = new RestTemplate();

        NLPInputToBeTransformed input = new NLPInputToBeTransformed();
        input.setInputText(" Test Input ");


        NLPResponse nlpResponse = restTemplate.postForObject
                (nlpServiceURL, input, NLPResponse.class, new HashMap<>());

        System.out.println( " Service Response  " + nlpResponse.getTags());