In case of any issue observed for getting the connection to Hadoop NameNode, below command can be used to verify the Hadoop metrics in which the Plugin will extract the State in active as a valid connection,

curl <HDFS_URL>/jmx?qry=Hadoop:service=NameNode,name=NameNodeStatus
* the HDFS_URL is the URL setting specified in HDFS Connection resource of the Plugin configuration.

A sample JSON output of the curl command like below,where we can see the State is ‘active’,

$ curl  http://ss01.na.tibco.com:50070/jmx?qry=Hadoop:service=NameNode,name=NameNodeStatus
{
  "beans" : [ {
    "name" : "Hadoop:service=NameNode,name=NameNodeStatus",
    "modelerType" : "org.apache.hadoop.hdfs.server.namenode.NameNode",
    "State" : "active",
    "NNRole" : "NameNode",
    "HostAndPort" : "ss01.na.tibco.com:8020",
    "SecurityEnabled" : true,
    "LastHATransitionTime" : 0,
    "BytesWithFutureGenerationStamps" : 0,
    "SlowPeersReport" : null,
    "SlowDisksReport" : null
  } ]