Update Eureka Server's service-urls upon EnvironmentChangeEvent. (#2455)

spring-cloud-netflix-eureka-server/src/main/java/org/springframework/cloud/netflix/eureka/server/EurekaServerAutoConfiguration.java

 /*
- * Copyright 2013-2015 the original author or authors.
+ * Copyright 2013-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,7 +35,9 @@ import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
 import org.springframework.cloud.client.actuator.HasFeatures;
+import org.springframework.cloud.context.environment.EnvironmentChangeEvent;
 import org.springframework.cloud.netflix.eureka.EurekaConstants;
+import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
 import org.springframework.context.annotation.Configuration;
@@ -67,6 +69,7 @@ import com.sun.jersey.spi.container.servlet.ServletContainer;
 /**
  * @author Gunnar Hillert
  * @author Biju Kunjummen
+ * @author Fahim Farook
  */
 @Configuration
 @Import(EurekaServerInitializerConfiguration.class)
@@ -169,10 +172,69 @@ public class EurekaServerAutoConfiguration extends WebMvcConfigurerAdapter {
 	@ConditionalOnMissingBean
 	public PeerEurekaNodes peerEurekaNodes(PeerAwareInstanceRegistry registry,
 			ServerCodecs serverCodecs) {
-		return new PeerEurekaNodes(registry, this.eurekaServerConfig,
+		return new RefreshablePeerEurekaNodes(registry, this.eurekaServerConfig,
 				this.eurekaClientConfig, serverCodecs, this.applicationInfoManager);
 	}
 	
+	/**
+	 * {@link PeerEurekaNodes} which updates peers when /refresh is invoked.
+	 * Peers are updated only if
+	 * <code>eureka.client.use-dns-for-fetching-service-urls</code> is
+	 * <code>false</code> and one of following properties have changed.
+	 * </p>
+	 * <ul>
+	 * <li><code>eureka.client.availability-zones</code></li>
+	 * <li><code>eureka.client.region</code></li>
+	 * <li><code>eureka.client.service-url.&lt;zone&gt;</code></li>
+	 * </ul>
+	 */
+	static class RefreshablePeerEurekaNodes extends PeerEurekaNodes
+			implements ApplicationListener<EnvironmentChangeEvent> {
+
+		public RefreshablePeerEurekaNodes(
+				final PeerAwareInstanceRegistry registry,
+				final EurekaServerConfig serverConfig,
+				final EurekaClientConfig clientConfig, 
+				final ServerCodecs serverCodecs,
+				final ApplicationInfoManager applicationInfoManager) {
+			super(registry, serverConfig, clientConfig, serverCodecs, applicationInfoManager);
+		}
+
+		@Override
+		public void onApplicationEvent(final EnvironmentChangeEvent event) {
+			if (shouldUpdate(event.getKeys())) {
+				updatePeerEurekaNodes(resolvePeerUrls());
+			}
+		}
+		
+		/*
+		 * Check whether specific properties have changed.
+		 */
+		protected boolean shouldUpdate(final Set<String> changedKeys) {
+			assert changedKeys != null;
+			
+			// if eureka.client.use-dns-for-fetching-service-urls is true, then
+			// service-url will not be fetched from environment.
+			if (clientConfig.shouldUseDnsForFetchingServiceUrls()) {
+				return false;
+			}
+			
+			if (changedKeys.contains("eureka.client.region")) {
+				return true;
+			}
+			
+			for (final String key : changedKeys) {
+				// property keys are not expected to be null.
+				if (key.startsWith("eureka.client.service-url.") ||
+					key.startsWith("eureka.client.availability-zones.")) {
+					return true;
+				}
+			}
+			
+			return false;
+		}
+	}
+
 	@Bean
 	public EurekaServerContext eurekaServerContext(ServerCodecs serverCodecs,
 			PeerAwareInstanceRegistry registry, PeerEurekaNodes peerEurekaNodes) {