Registering multiple instances in Eureka from one application

MultipleEurekaInstanceApplication.java

package com.myorg;

import com.netflix.appinfo.ApplicationInfoManager;
import com.netflix.appinfo.InstanceInfo;
import com.netflix.discovery.AbstractDiscoveryClientOptionalArgs;
import com.netflix.discovery.DiscoveryClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.cloud.commons.util.InetUtils;
import org.springframework.cloud.commons.util.InetUtilsProperties;
import org.springframework.cloud.netflix.eureka.EurekaClientConfigBean;
import org.springframework.cloud.netflix.eureka.EurekaInstanceConfigBean;
import org.springframework.cloud.netflix.eureka.InstanceInfoFactory;
import org.springframework.cloud.netflix.eureka.serviceregistry.EurekaServiceRegistry;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Bean;
import org.springframework.context.event.ContextClosedEvent;

import java.util.HashSet;
import java.util.Set;
import java.util.UUID;

@SpringBootApplication
public class MultipleEurekaInstanceApplication
{
   private final static Logger ourLogger =
      LoggerFactory.createLogger(MultipleEurekaInstanceApplication.class);

   /**
    * Eureka application name / instance prefix
    */
   private final static String APPLICATION_NAME = "my-app";

   @Autowired
   private EurekaInstanceConfigBean originalInstanceConfig;

   @Autowired
   private EurekaClientConfigBean originalClientConfig;

   @Autowired
   private ApplicationInfoManager applicationInfoManager;

   @Autowired
   private ApplicationContext context;

   @Autowired
   private AbstractDiscoveryClientOptionalArgs args;

   @Value("${HOSTNAME}")
   private String hostName;

   @Value("${my.app.numInstances:5}")
   private int numInstances;

   /**
    * These are the DiscoverClient objects we manage ourselves
    */
   private Set<DiscoveryClient> discoveryClients = new HashSet<>();

   public static void main(String[] args)
   {
      SpringApplication.run(MultipleEurekaInstanceApplication.class, args);
   }

   /**
    * Responsible for registering <code>my.app.numInstances</code> number
    * of instances in Eureka for use by session manager. Waits until the
    * application context is ready to create the registrations.
    *
    * @return
    */
   @Bean
   public ApplicationListener applicationListener()
   {
      return applicationEvent -> {
         if(applicationEvent instanceof ApplicationReadyEvent)
         {
            if(numInstances < 1)
            {
               numInstances = 1;
            }

            //
            // We get 1 session for free with Spring Cloud Eureka, so we only need
            // to register (numInstances - 1) new instances.
            //

            for(int i = 1; i < numInstances; i++)
            {
               //
               // Simply creating the DiscoveryClient is enough to force
               // registration. We hold on to the reference for later use
               // so we can unregister during shutdown.
               //

               DiscoveryClient discoveryClient =
                  new DiscoveryClient(
                     duplicateAppInfoManager(),
                     duplicateConfig(),
                     args);
               discoveryClients.add(discoveryClient);
            }
         }
      };
   }

   /**
    * Handles forcing all the extra instances we register to DOWN state when the
    * application is terminated.
    */
   @Bean
   public ApplicationListener discoveryClientShutdownListener()
   {
      return applicationEvent -> {
         if(applicationEvent instanceof ContextClosedEvent)
         {
            for(DiscoveryClient client: discoveryClients)
            {
               ourLogger.info("Shutting down discovery client for " + client.getApplicationInfoManager().getEurekaInstanceConfig().getInstanceId());
               client.shutdown();
            }
         }
      };
   }

   //
   // These duplicateXXX methods are used to create copies of the
   // various Eureka beans that the Spring Cloud auto config
   // creates for us.
   //

   private ApplicationInfoManager duplicateAppInfoManager()
   {
      EurekaInstanceConfigBean newInstanceConfig =
         new EurekaInstanceConfigBean(new InetUtils(new InetUtilsProperties()));

      newInstanceConfig.setEnvironment(context.getEnvironment());
      newInstanceConfig.setAppname(APPLICATION_NAME);
      newInstanceConfig.setInstanceId(APPLICATION_NAME + ":" + hostName + ":" + UUID.randomUUID().toString());
      newInstanceConfig.setInitialStatus(InstanceInfo.InstanceStatus.UP);
      newInstanceConfig.setNonSecurePortEnabled(originalInstanceConfig.isNonSecurePortEnabled());
      newInstanceConfig.setNonSecurePort(originalInstanceConfig.getNonSecurePort());
      newInstanceConfig.setSecurePortEnabled(originalInstanceConfig.isSecurePortEnabled());
      newInstanceConfig.setSecurePort(originalInstanceConfig.getSecurePort());
      newInstanceConfig.setDataCenterInfo(originalInstanceConfig.getDataCenterInfo());
      newInstanceConfig.setHealthCheckUrl(originalInstanceConfig.getHealthCheckUrl());
      newInstanceConfig.setSecureHealthCheckUrl(originalInstanceConfig.getSecureHealthCheckUrl());
      newInstanceConfig.setHomePageUrl(originalInstanceConfig.getHomePageUrl());
      newInstanceConfig.setStatusPageUrl(originalInstanceConfig.getStatusPageUrl());
      newInstanceConfig.setStatusPageUrlPath(originalInstanceConfig.getStatusPageUrlPath());
      newInstanceConfig.setIpAddress(originalInstanceConfig.getIpAddress());
      newInstanceConfig.setPreferIpAddress(originalInstanceConfig.isPreferIpAddress());

      ApplicationInfoManager manager =
         new ApplicationInfoManager(
            newInstanceConfig,
            duplicateInstanceInfo(applicationInfoManager.getInfo()));

      return manager;
   }

   private InstanceInfo duplicateInstanceInfo(InstanceInfo info)
   {
      //
      // Temporarily swap the instance ID; have to restore so that the bean
      // created in the auto configs keeps it original ID.
      //

      String originalId = originalInstanceConfig.getInstanceId();

      originalInstanceConfig.setInstanceId(SESSION_SERVER_NAME + ":" + hostName + ":" + UUID.randomUUID().toString());
      InstanceInfo newInfo = new InstanceInfoFactory().create(originalInstanceConfig);
      newInfo.setStatus(InstanceInfo.InstanceStatus.UP);
      originalInstanceConfig.setInstanceId(originalId);

      return newInfo;
   }

   private EurekaClientConfigBean duplicateConfig()
   {
      EurekaClientConfigBean newConfig = new EurekaClientConfigBean();
      newConfig.setFetchRegistry(false);
      newConfig.setEurekaServerPort(originalClientConfig.getEurekaServerPort());
      newConfig.setAllowRedirects(originalClientConfig.isAllowRedirects());
      newConfig.setAvailabilityZones(originalClientConfig.getAvailabilityZones());
      newConfig.setBackupRegistryImpl(originalClientConfig.getBackupRegistryImpl());
      newConfig.setServiceUrl(originalClientConfig.getServiceUrl());
      return newConfig;
   }
}

This assumes you have Spring Cloud Eureka configured to register an instance automatically:

eureka.client.register-with-eureka=true
eureka.instance.appname=my-app
eureka.instance.instance-id=my-app:${HOSTNAME}:${random.uuid}