When the local NameNode is healthy, the ZKFC holds a session open in ZooKeeper. If the local NameNode is active, it also holds a special “lock” znode. This lock uses ZooKeeper’s support for “ephemeral” nodes; if the session expires, the lock node will be automatically deleted. Ephemeral znodes - These znodes exists as long as the session that created the znode is active. When the session ends the znode is deleted. Zookeeper has a concept of Watches which can be set on znodes to track them for any changes. Check the link how Watches work in zookeeper - https://zookeeper.apache.org/doc/current/zookeeperProgrammers.html#ch_zkWatches ... View more

We cannot set specfic configuration to only handle replication related jobs with separate NIC in HDFS. However, we can setup a multi-homed environment for datanodes for all the traffic for specific datanodes. Kindly check below documentation for the same - https://hadoop.apache.org/docs/r2.7.1/hadoop-project-dist/hadoop-hdfs/HdfsMultihoming.html ... View more

@George-Megre  The Master nodes firstly are not meant for launching tasks or interaction.  Edge or gateway nodes are used to run client applications and cluster administration tools. Setup of Edge/gateway node is similar to any Hadoop node except no Hadoop cluster services runs on the GW/Edge nodes they are mere entry points and connection gateway to the Master Components like HDFS (NN) HBASE etc provide you have installed the client libraries.   In your case, I am sure you have the Hbase client/gateway roles on the 3 nodes and not on the master noded. The HBase client role gives the connectivity to Hbase but again I don't see why you would like to connect /initiate the HBase shell from the master node? Geoffrey ... View more