Fix server host resolution when host is configured

pinot-server/src/main/java/org/apache/pinot/server/starter/helix/BaseServerStarter.java

@@ -219,9 +219,7 @@ public void init(PinotConfiguration serverConf)
 
     setupHelixSystemProperties();
     _listenerConfigs = ListenerConfigUtil.buildServerAdminConfigs(_serverConf);
-    _hostname = _serverConf.getProperty(Helix.KEY_OF_SERVER_NETTY_HOST,
-        _serverConf.getProperty(Helix.SET_INSTANCE_ID_TO_HOSTNAME_KEY, false) ? NetUtils.getHostnameOrAddress()
-            : NetUtils.getHostAddress());
+    _hostname = getServerHostname(_serverConf);
     // Override multi-stage query runner hostname if not set explicitly
     if (!_serverConf.containsKey(CommonConstants.MultiStageQueryRunner.KEY_OF_QUERY_RUNNER_HOSTNAME)) {
       _serverConf.setProperty(CommonConstants.MultiStageQueryRunner.KEY_OF_QUERY_RUNNER_HOSTNAME, _hostname);
@@ -323,6 +321,17 @@ protected QueryOperatorFactoryProvider createQueryOperatorFactoryProvider(PinotC
     return DefaultQueryOperatorFactoryProvider.INSTANCE;
   }
 
+  @VisibleForTesting
+  static String getServerHostname(PinotConfiguration serverConf)
+      throws IOException {
+    String configuredHost = serverConf.getProperty(Helix.KEY_OF_SERVER_NETTY_HOST);
+    if (configuredHost != null) {
+      return configuredHost;
+    }
+    return serverConf.getProperty(Helix.SET_INSTANCE_ID_TO_HOSTNAME_KEY, false) ? NetUtils.getHostnameOrAddress()
+        : NetUtils.getHostAddress();
+  }
+
   /**
    *  Invoke pinot environment provider factory's init method to register the environment provider &
    *  return the instantiated environment provider.

pinot-server/src/test/java/org/apache/pinot/server/starter/helix/BaseServerStarterTest.java

@@ -0,0 +1,79 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.pinot.server.starter.helix;
+
+import org.apache.pinot.spi.env.PinotConfiguration;
+import org.apache.pinot.spi.utils.CommonConstants.Helix;
+import org.apache.pinot.spi.utils.NetUtils;
+import org.mockito.MockedStatic;
+import org.testng.annotations.Test;
+
+import static org.mockito.Mockito.mockStatic;
+import static org.mockito.Mockito.never;
+import static org.testng.Assert.assertEquals;
+
+public class BaseServerStarterTest {
+  @Test
+  public void testConfiguredServerHostDoesNotResolveDefaultHost()
+      throws Exception {
+    PinotConfiguration serverConf = new PinotConfiguration();
+    serverConf.setProperty(Helix.KEY_OF_SERVER_NETTY_HOST, "pinot-server-node1");
+
+    try (MockedStatic<NetUtils> netUtils = mockStatic(NetUtils.class)) {
+      netUtils.when(NetUtils::getHostAddress).thenThrow(new AssertionError("Should not resolve host address"));
+      netUtils.when(NetUtils::getHostnameOrAddress).thenThrow(new AssertionError("Should not resolve hostname"));
+
+      assertEquals(BaseServerStarter.getServerHostname(serverConf), "pinot-server-node1");
+
+      netUtils.verify(NetUtils::getHostAddress, never());
+      netUtils.verify(NetUtils::getHostnameOrAddress, never());
+    }
+  }
+
+  @Test
+  public void testServerHostFallsBackToHostAddress()
+      throws Exception {
+    PinotConfiguration serverConf = new PinotConfiguration();
+
+    try (MockedStatic<NetUtils> netUtils = mockStatic(NetUtils.class)) {
+      netUtils.when(NetUtils::getHostAddress).thenReturn("10.0.0.1");
+
+      assertEquals(BaseServerStarter.getServerHostname(serverConf), "10.0.0.1");
+
+      netUtils.verify(NetUtils::getHostAddress);
+      netUtils.verify(NetUtils::getHostnameOrAddress, never());
+    }
+  }
+
+  @Test
+  public void testServerHostFallsBackToHostnameWhenConfigured()
+      throws Exception {
+    PinotConfiguration serverConf = new PinotConfiguration();
+    serverConf.setProperty(Helix.SET_INSTANCE_ID_TO_HOSTNAME_KEY, true);
+
+    try (MockedStatic<NetUtils> netUtils = mockStatic(NetUtils.class)) {
+      netUtils.when(NetUtils::getHostnameOrAddress).thenReturn("pinot-server-node1");
+
+      assertEquals(BaseServerStarter.getServerHostname(serverConf), "pinot-server-node1");
+
+      netUtils.verify(NetUtils::getHostnameOrAddress);
+      netUtils.verify(NetUtils::getHostAddress, never());
+    }
+  }
+}