HDFS-8196. Post enabled Erasure Coding Policies on NameNode UI. Contributed by Kitti Nanasi and Kai Sasaki.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/ErasureCodingPolicyManager.java

@@ -31,6 +31,7 @@ import org.apache.hadoop.hdfs.protocol.HdfsConstants;
 
 import org.apache.hadoop.io.erasurecode.CodecUtil;
 import org.apache.hadoop.io.erasurecode.ErasureCodeConstants;
+import org.apache.hadoop.util.StringUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -430,4 +431,9 @@ public final class ErasureCodingPolicyManager {
     allPolicies =
         policiesByName.values().toArray(new ErasureCodingPolicyInfo[0]);
   }
+
+  public String getEnabledPoliciesMetric() {
+    return StringUtils.join(", ",
+            enabledPoliciesByName.keySet());
+  }
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -4973,6 +4973,15 @@ public class FSNamesystem implements Namesystem, FSNamesystemMBean,
     return blockManager.getTotalECBlockGroups();
   }
 
+  /**
+   * Get the enabled erasure coding policies separated with comma.
+   */
+  @Override // ECBlockGroupsMBean
+  @Metric({"EnabledEcPolicies", "Enabled erasure coding policies"})
+  public String getEnabledEcPolicies() {
+    return getErasureCodingPolicyManager().getEnabledPoliciesMetric();
+  }
+
   @Override
   public long getBlockDeletionStartTime() {
     return startTime + blockManager.getStartupDelayBlockDeletionInMs();

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/metrics/ECBlockGroupsMBean.java

@@ -61,4 +61,9 @@ public interface ECBlockGroupsMBean {
    * Return total number of erasure coded block groups.
    */
   long getTotalECBlockGroups();
+
+  /**
+   * @return the enabled erasure coding policies separated with comma.
+   */
+  String getEnabledEcPolicies();
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/webapps/hdfs/dfshealth.html

@@ -186,10 +186,12 @@
   {/eq}
   <tr><th>Block Deletion Start Time</th><td>{BlockDeletionStartTime|date_tostring}</td></tr>
 {/fs}
-
 {#fsn}
   <tr><th>Last Checkpoint Time</th><td>{@if cond="{LastCheckpointTime} === 0"}Never{:else}{LastCheckpointTime|date_tostring}{/if}</td></tr>
 {/fsn}
+{#ecstat}
+  <tr><th>Enabled Erasure Coding Policies</th><td>{EnabledEcPolicies}</td></tr>
+{/ecstat}
 </table>
 
 <div class="page-header"><h1>NameNode Journal Status</h1></div>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/namenode/TestNameNodeMXBean.java

@@ -34,6 +34,7 @@ import org.apache.hadoop.hdfs.MiniDFSCluster;
 import org.apache.hadoop.hdfs.MiniDFSNNTopology;
 import org.apache.hadoop.hdfs.StripedFileTestUtil;
 import org.apache.hadoop.hdfs.protocol.DatanodeInfo;
+import org.apache.hadoop.hdfs.protocol.ErasureCodingPolicy;
 import org.apache.hadoop.hdfs.protocol.HdfsConstants.SafeModeAction;
 import org.apache.hadoop.hdfs.protocol.LocatedBlock;
 import org.apache.hadoop.hdfs.protocol.LocatedStripedBlock;
@@ -728,6 +729,46 @@ public class TestNameNodeMXBean {
     }
   }
 
+  @Test
+  public void testEnabledEcPoliciesMetric() throws Exception {
+    MiniDFSCluster cluster = null;
+    DistributedFileSystem fs = null;
+    try {
+      Configuration conf = new HdfsConfiguration();
+
+      ErasureCodingPolicy defaultPolicy =
+          StripedFileTestUtil.getDefaultECPolicy();
+      int dataBlocks = defaultPolicy.getNumDataUnits();
+      int parityBlocks = defaultPolicy.getNumParityUnits();
+      int totalSize = dataBlocks + parityBlocks;
+      cluster = new MiniDFSCluster.Builder(conf)
+          .numDataNodes(totalSize).build();
+      fs = cluster.getFileSystem();
+
+      final String defaultPolicyName = defaultPolicy.getName();
+      final String rs104PolicyName = "RS-10-4-1024k";
+
+      assertEquals("Enabled EC policies metric should return with " +
+          "the default EC policy", defaultPolicyName,
+          getEnabledEcPoliciesMetric());
+
+      fs.enableErasureCodingPolicy(rs104PolicyName);
+      assertEquals("Enabled EC policies metric should return with " +
+              "both enabled policies separated by a comma",
+          rs104PolicyName + ", " + defaultPolicyName,
+          getEnabledEcPoliciesMetric());
+
+      fs.disableErasureCodingPolicy(defaultPolicyName);
+      fs.disableErasureCodingPolicy(rs104PolicyName);
+      assertEquals("Enabled EC policies metric should return with " +
+          "an empty string if there is no enabled policy",
+          "", getEnabledEcPoliciesMetric());
+    } finally {
+      fs.close();
+      cluster.shutdown();
+    }
+  }
+
   @Test
   public void testVerifyMissingBlockGroupsMetrics() throws Exception {
     MiniDFSCluster cluster = null;
@@ -968,4 +1009,12 @@ public class TestNameNodeMXBean {
     assertEquals("Unexpected total ec block groups!",
         expectedTotalECBlockGroups, totalECBlockGroups.longValue());
   }
+
+  private String getEnabledEcPoliciesMetric() throws Exception {
+    MBeanServer mbs = ManagementFactory.getPlatformMBeanServer();
+    ObjectName mxbeanName = new ObjectName(
+        "Hadoop:service=NameNode,name=ECBlockGroupsState");
+    return (String) (mbs.getAttribute(mxbeanName,
+        "EnabledEcPolicies"));
+  }
 }