@karthik nedunchezhiyan A simplified explanation of the process : Whenever a NN HA is achieved, there will be two NNs , One Active NN and other Standby NN, 1) DataNodes will send heartbeats to both NNs , so both Active and Standby will know where the blocks are placed. 2) Journal Nodes maintain the Shared edits , Whenever there is a write operation the JNs will update the edits, not the Active or Standby NN. Once the edits are updated by JN, the Standby will update its FS Image. 3)So this way at any point in time both the Active and the Standby will have the same updated FS Image. 4)Zookeeper will be responsible for holding the lock for the Active NN. 5) There will be two Zookeeper Failover Controllers, which will be responsible for monitoring the health of the NNs. 6) Whenever the Zookeeper does not receive a communication from the Zookeeper FC, it will release the lock and this will be acquired by the other Zookeeper FC and the Standby NN will become the Active NN.
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