Allow proxy mode server name to be updated (#54107)

Currently there is a bug where the proxy strategy will not be rebuilt if
the server_name is dynamically updated. This commit fixes this issue.

Author: Tim-Brooks

server/src/main/java/org/elasticsearch/transport/ProxyConnectionStrategy.java

@@ -157,7 +157,9 @@ protected boolean shouldOpenMoreConnections() {
     protected boolean strategyMustBeRebuilt(Settings newSettings) {
         String address = PROXY_ADDRESS.getConcreteSettingForNamespace(clusterAlias).get(newSettings);
         int numOfSockets = REMOTE_SOCKET_CONNECTIONS.getConcreteSettingForNamespace(clusterAlias).get(newSettings);
-        return numOfSockets != maxNumConnections || configuredAddress.equals(address) == false;
+        String serverName = SERVER_NAME.getConcreteSettingForNamespace(clusterAlias).get(newSettings);
+        return numOfSockets != maxNumConnections || configuredAddress.equals(address) == false ||
+            Objects.equals(serverName, configuredServerName) == false;
     }
 
     @Override

server/src/test/java/org/elasticsearch/transport/ProxyConnectionStrategyTests.java

@@ -268,7 +268,7 @@ public void testProxyStrategyWillResolveAddressesEachConnect() throws Exception
         }
     }
 
-    public void testProxyStrategyWillNeedToBeRebuiltIfNumOfSocketsOrAddressesChange() {
+    public void testProxyStrategyWillNeedToBeRebuiltIfNumOfSocketsOrAddressesOrServerNameChange() {
         try (MockTransportService remoteTransport = startTransport("node1", Version.CURRENT)) {
             TransportAddress remoteAddress = remoteTransport.boundAddress().publishAddress();
 
@@ -280,7 +280,7 @@ public void testProxyStrategyWillNeedToBeRebuiltIfNumOfSocketsOrAddressesChange(
                 int numOfConnections = randomIntBetween(4, 8);
                 try (RemoteConnectionManager remoteConnectionManager = new RemoteConnectionManager(clusterAlias, connectionManager);
                      ProxyConnectionStrategy strategy = new ProxyConnectionStrategy(clusterAlias, localService, remoteConnectionManager,
-                         numOfConnections, remoteAddress.toString())) {
+                         numOfConnections, remoteAddress.toString(), "server-name")) {
                     PlainActionFuture<Void> connectFuture = PlainActionFuture.newFuture();
                     strategy.connect(connectFuture);
                     connectFuture.actionGet();
@@ -295,11 +295,14 @@ public void testProxyStrategyWillNeedToBeRebuiltIfNumOfSocketsOrAddressesChange(
                         .getConcreteSettingForNamespace("cluster-alias");
                     Setting<?> socketConnections = ProxyConnectionStrategy.REMOTE_SOCKET_CONNECTIONS
                         .getConcreteSettingForNamespace("cluster-alias");
+                    Setting<?> serverName = ProxyConnectionStrategy.SERVER_NAME
+                        .getConcreteSettingForNamespace("cluster-alias");
 
                     Settings noChange = Settings.builder()
                         .put(modeSetting.getKey(), "proxy")
                         .put(addressesSetting.getKey(), remoteAddress.toString())
                         .put(socketConnections.getKey(), numOfConnections)
+                        .put(serverName.getKey(), "server-name")
                         .build();
                     assertFalse(strategy.shouldRebuildConnection(noChange));
                     Settings addressesChanged = Settings.builder()
@@ -313,6 +316,13 @@ public void testProxyStrategyWillNeedToBeRebuiltIfNumOfSocketsOrAddressesChange(
                         .put(socketConnections.getKey(), numOfConnections + 1)
                         .build();
                     assertTrue(strategy.shouldRebuildConnection(socketsChanged));
+                    Settings serverNameChange = Settings.builder()
+                        .put(modeSetting.getKey(), "proxy")
+                        .put(addressesSetting.getKey(), remoteAddress.toString())
+                        .put(socketConnections.getKey(), numOfConnections)
+                        .put(serverName.getKey(), "server-name2")
+                        .build();
+                    assertTrue(strategy.shouldRebuildConnection(serverNameChange));
                 }
             }
         }