HDDS-16018. Use configured DNS-to-switch mapping directly in SCM

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/StorageContainerManager.java

@@ -181,7 +181,6 @@
 import org.apache.hadoop.ipc_.RPC;
 import org.apache.hadoop.metrics2.MetricsSystem;
 import org.apache.hadoop.metrics2.util.MBeans;
-import org.apache.hadoop.net.CachedDNSToSwitchMapping;
 import org.apache.hadoop.net.DNSToSwitchMapping;
 import org.apache.hadoop.net.NetUtils;
 import org.apache.hadoop.net.ScriptBasedMapping;
@@ -755,15 +754,7 @@ private void initializeSystemManagers(OzoneConfiguration conf,
           .build();
     }
 
-    Class<? extends DNSToSwitchMapping> dnsToSwitchMappingClass =
-        conf.getClass(
-            ScmConfigKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY,
-            ScriptBasedMapping.class, DNSToSwitchMapping.class);
-    DNSToSwitchMapping newInstance = ReflectionUtils.newInstance(
-        dnsToSwitchMappingClass, conf);
-    dnsToSwitchMapping =
-        ((newInstance instanceof CachedDNSToSwitchMapping) ? newInstance
-            : new CachedDNSToSwitchMapping(newInstance));
+    dnsToSwitchMapping = createDNSToSwitchMapping(conf);
 
     if (configurator.getScmNodeManager() != null) {
       scmNodeManager = configurator.getScmNodeManager();
@@ -2375,4 +2366,12 @@ public String resolveNodeLocation(String hostname) {
     }
   }
 
+  static DNSToSwitchMapping createDNSToSwitchMapping(OzoneConfiguration conf) {
+    Class<? extends DNSToSwitchMapping> mappingClass =
+        conf.getClass(
+            ScmConfigKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY,
+            ScriptBasedMapping.class, DNSToSwitchMapping.class);
+    return ReflectionUtils.newInstance(mappingClass, conf);
+  }
+
 }

hadoop-hdds/server-scm/src/test/java/org/apache/hadoop/hdds/scm/server/TestStorageContainerManager.java

@@ -0,0 +1,56 @@
+/*
+ * 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.hadoop.hdds.scm.server;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+
+import org.apache.hadoop.hdds.conf.OzoneConfiguration;
+import org.apache.hadoop.hdds.scm.ScmConfigKeys;
+import org.apache.hadoop.net.CachedDNSToSwitchMapping;
+import org.apache.hadoop.net.DNSToSwitchMapping;
+import org.apache.hadoop.net.ScriptBasedMapping;
+import org.apache.hadoop.net.StaticMapping;
+import org.junit.jupiter.api.Test;
+
+class TestStorageContainerManager {
+
+  @Test
+  void defaultMappingKeepsCachedBehavior() {
+    DNSToSwitchMapping mapping =
+        StorageContainerManager.createDNSToSwitchMapping(
+            new OzoneConfiguration());
+
+    assertInstanceOf(ScriptBasedMapping.class, mapping);
+    assertInstanceOf(CachedDNSToSwitchMapping.class, mapping);
+  }
+
+  @Test
+  void configuredMappingIsUsedDirectly() {
+    OzoneConfiguration conf = new OzoneConfiguration();
+    conf.setClass(ScmConfigKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY,
+        StaticMapping.class, DNSToSwitchMapping.class);
+
+    DNSToSwitchMapping mapping =
+        StorageContainerManager.createDNSToSwitchMapping(conf);
+
+    assertInstanceOf(StaticMapping.class, mapping);
+    assertFalse(mapping instanceof CachedDNSToSwitchMapping,
+        "Configured mapping should not be wrapped in CachedDNSToSwitchMapping");
+  }
+}