Active NN on machine1
Standby NN on machine2
Machine1 is isolated from the network (machine1 network cable unplugged)
After zk session timeout ZKFC at machine2 side gets notification that NN1 is not there.
ZKFC tries to failover NN2 as active.
As part of this during fencing it tries to connect to machine1 and kill NN1. (sshfence technique configured)
This connection retry happens for 45 times( as it takes ipc.client.connect.max.socket.retries)
Also after that standby NN is not able to take over as active (because of fencing failure).
Suggestion: If ZKFC is not able to reach other NN for specified time/no of retries it can consider that NN as dead and instruct the other NN to take over as active as there is no chance of the other NN (NN1) retaining its state as active after zk session timeout when its isolated from network
From ZKFC log: