@Lokesh Mukku In a Namenode HA there is no notion of IP address but Nameservice ID (geeklab)as illustrated in the screenshot. In the background, geeklab will be doing something like load balancing between (nn01,nn02) whichever is the Active at a particular time, for example, if nn01 is the active NN and all over a sudden it encounters an issue and goes down, the ZKFailoverController will detect that failure through the heartbeat misses and transparently failover to nn02. The Nameservice ID is used to avoid hard-coding the IP's in case you change the host during an upgrade or system failure. I gave you the example of DNS to explain it further..www.teamworks.com is a DNS entry used to resolve hostnames to a specific IP of the teamworks.com web server to machine-readable IP addresses (e.g. 192.168.106.81) behind the scenes www.teamworks.com to guard against any failure could have a couple of web servers (HA setup ) say 3 web servers serving content for www.teamworks.com with a load balancer (see screenshot LB.png) which act like the Nameservice ID in case a namenode/web server goes down the cluster/website will still be available as Nameservice ID will automatically failover point to the active name node controlled by ZKFailoverController . HTH
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