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I have a zookeeper ensemble running in Kubernetes consisting of 3 instances. The ensemble operates mostly correctly and successfully services the Solr cluster it is backing. One thing does seem incorrect however, and it's breaking some health checks in another part of my application (Sitecore) as a result.

For some reason, the Solr -> Cloud -> ZK Status page -AND- the mntr command on the leader itself report sporadically changing and incorrect numbers of followers:

Solr GUI error

root@zk-1:/zookeeper-3.4.14# echo mntr | nc localhost 2181
zk_version      3.4.14-4c25d480e66aadd371de8bd2fd8da255ac140bcf, built on 03/06/2019 16:18 GMT
zk_avg_latency  2
zk_max_latency  4
zk_min_latency  1
zk_packets_received     1132
zk_packets_sent 1131
zk_num_alive_connections        5
zk_outstanding_requests 0
zk_server_state leader
zk_znode_count  1405
zk_watch_count  0
zk_ephemerals_count     57
zk_approximate_data_size        4703048
zk_open_file_descriptor_count   42
zk_max_file_descriptor_count    1048576
zk_fsync_threshold_exceed_count 0
zk_followers    5
zk_synced_followers     2
zk_pending_syncs        0
zk_last_proposal_size   92
zk_max_proposal_size    55791
zk_min_proposal_size    32

Note the number of reported followers (zk_followers) is not consistent - in this sample the GUI reports 4 but the command line reports 5. This number jumps up and down every time I refresh the GUI or re-run the mntr command, usually anywhere from 3-6 (the correct result obviously should be 2)

I can't work out what these extra followers being reported could be, as no output other than the zk_followers var shows anything other than the two real ones and logs don't seem to report anything untoward.

zoo.cfg:

root@zk-1:/zookeeper-3.4.14# cat /conf/zoo.cfg
clientPort=2181
dataDir=/store/data        
dataLogDir=/store/datalog  
tickTime=2000
initLimit=5
syncLimit=2
autopurge.snapRetainCount=3
autopurge.purgeInterval=0  
maxClientCnxns=60
server.1=zk-0.zk:2888:3888 
server.2=0.0.0.0:2888:3888 
server.3=zk-2.zk:2888:3888

zooservers.txt:

root@zk-1:/zookeeper-3.4.14# cat /conf/zooservers.txt 
server.1=zk-0.zk:2888:3888 server.2=0.0.0.0:2888:3888 server.3=zk-2.zk:2888:3888

As noted this doesn't seem to cause any real problems with the ensemble or the solr cluster except that it's failing some container start health checks which cause inconsistency in the application, and could potentially bring down parts of it.

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  • The server.2=0.0.0.0:2888:3888 is quite confusing entry. It should be the server.2=zk-1.zk:2888:3888
    – kofemann
    Dec 2 '20 at 14:51
  • I should point out, that's the config FROM zk-1 (i.e. server 2). Each server refers to itself in its config as 0.0.0.0 - this is Zookeeper standard.
    – Taz
    Dec 2 '20 at 23:17

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