When restarting our ensemble of zookeepers, I restart the leader last (to avoid repeatedly reallocating the role). Which means I’ve got to find the leader. Luckily the zookeepers are happy to report if they are the leader or a follower if you send ‘srvr’ to the zookeeper port.

jumpserver:~ # echo srvr | nc zcserver38.example.net 2181
Zookeeper version: 3.5.8-f439ca583e70862c3068a1f2a7d4d068eec33315, built on 05/04/2020 15:53 GMT
Latency min/avg/max: 0/0/1383
Received: 3783871
Sent: 3784761
Connections: 7
Outstanding: 0
Zxid: 0x800003d25
Mode: follower
Node count: 3715

Looking at the “Mode” line above, I can see that’s the follower. So I’ll check the next Zookeeper …

jumpserver:~ # echo srvr | nc zcserver39.example.net 2181
Zookeeper version: 3.5.8-f439ca583e70862c3068a1f2a7d4d068eec33315, built on 05/04/2020 15:53 GMT
Latency min/avg/max: 0/0/1167
Received: 836866
Sent: 848235
Connections: 1
Outstanding: 0
Zxid: 0x800003d25
Mode: leader
Node count: 3715
Proposal sizes last/min/max: 36/32/19782

And that’s the leader — so 39 will be the last one rebooted.