YARN-6104. RegistrySecurity overrides zookeeper sasl system properties. Contributed by Billie Rinaldi

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-registry/src/main/java/org/apache/hadoop/registry/client/impl/zk/RegistrySecurity.java

@@ -749,8 +749,15 @@ public class RegistrySecurity extends AbstractService {
       String context)  {
     RegistrySecurity.validateContext(context);
     enableZookeeperClientSASL();
-    System.setProperty(PROP_ZK_SASL_CLIENT_USERNAME, username);
-    System.setProperty(PROP_ZK_SASL_CLIENT_CONTEXT, context);
+    setSystemPropertyIfUnset(PROP_ZK_SASL_CLIENT_USERNAME, username);
+    setSystemPropertyIfUnset(PROP_ZK_SASL_CLIENT_CONTEXT, context);
+  }
+
+  private static void setSystemPropertyIfUnset(String name, String value) {
+    String existingValue = System.getProperty(name);
+    if (existingValue == null || existingValue.isEmpty()) {
+      System.setProperty(name, value);
+    }
   }
 
   /**

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-registry/src/test/java/org/apache/hadoop/registry/secure/TestSecureRegistry.java

@@ -37,6 +37,8 @@ import javax.security.auth.login.AppConfigurationEntry;
 import javax.security.auth.login.LoginContext;
 
 import static org.apache.hadoop.registry.client.api.RegistryConstants.*;
+import static org.apache.hadoop.registry.client.impl.zk.ZookeeperConfigOptions.PROP_ZK_SASL_CLIENT_CONTEXT;
+import static org.apache.hadoop.registry.client.impl.zk.ZookeeperConfigOptions.PROP_ZK_SASL_CLIENT_USERNAME;
 
 /**
  * Verify that the Mini ZK service can be started up securely
@@ -138,6 +140,26 @@ public class TestSecureRegistry extends AbstractSecureRegistryTest {
     }
   }
 
+  @Test
+  public void testSystemPropertyOverwrite() {
+    System.setProperty(PROP_ZK_SASL_CLIENT_USERNAME, "");
+    System.setProperty(PROP_ZK_SASL_CLIENT_CONTEXT, "");
+    RegistrySecurity.setZKSaslClientProperties(ZOOKEEPER,
+        ZOOKEEPER_CLIENT_CONTEXT);
+    assertEquals(ZOOKEEPER, System.getProperty(PROP_ZK_SASL_CLIENT_USERNAME));
+    assertEquals(ZOOKEEPER_CLIENT_CONTEXT,
+        System.getProperty(PROP_ZK_SASL_CLIENT_CONTEXT));
+
+    String userName = "user1";
+    String context = "context1";
+    System.setProperty(PROP_ZK_SASL_CLIENT_USERNAME, userName);
+    System.setProperty(PROP_ZK_SASL_CLIENT_CONTEXT, context);
+    RegistrySecurity.setZKSaslClientProperties(ZOOKEEPER,
+        ZOOKEEPER_CLIENT_CONTEXT);
+    assertEquals(userName, System.getProperty(PROP_ZK_SASL_CLIENT_USERNAME));
+    assertEquals(context, System.getProperty(PROP_ZK_SASL_CLIENT_CONTEXT));
+  }
+
   /**
    * Start a curator service instance
    * @param name name