Zookeeper 4 letters words admin commands

In this article we will discover Zookeeper 4 letters commands to help us to monitor Zookeper

How to send 4 letters words commands to Zookeeper

You will find all the ZK 4 letters words commands in the Administrator documentation

The more interesting in my point of view are mntr, stat and wchc.

For sending the command you have to know your Zookeeper servers hostnames and port (usually 2181) and use the nc command to access to the Zookeeper server.

As you can see there is no security about authentification on the ZK server when using those 4lw commands, we will see below how to manage that.

[zookeeper@sandbox-hdp ~]$ echo mntr | nc zk_hostname 2181
zk_version	3.4.6-292--1, built on 05/11/2018 07:15 GMT
zk_avg_latency	3
zk_max_latency	4073
zk_min_latency	0
zk_packets_received	58670
zk_packets_sent	58714
zk_num_alive_connections	19
zk_outstanding_requests	0
zk_server_state	standalone
zk_znode_count	318
zk_watch_count	71
zk_ephemerals_count	12
zk_approximate_data_size	102703
zk_open_file_descriptor_count	73
zk_max_file_descriptor_count	65536

[zookeeper@sandbox-hdp ~]$ echo stat|nc localhost 2181
Zookeeper version: 3.4.6-292--1, built on 05/11/2018 07:15 GMT
Clients:
 /172.18.0.2:34318[1](queued=0,recved=6769,sent=6769)
 /172.18.0.3:34308[0](queued=0,recved=1,sent=0)
 /172.18.0.2:33512[1](queued=0,recved=585,sent=585)
 /172.18.0.2:54036[1](queued=0,recved=1535,sent=1542)
 /172.18.0.2:59180[1](queued=0,recved=1332,sent=1334)
 /172.18.0.2:58414[1](queued=0,recved=602,sent=602)
 /172.18.0.2:59492[1](queued=0,recved=1020,sent=1020)
 /172.18.0.2:58322[1](queued=0,recved=515,sent=515)
 /172.18.0.2:59486[1](queued=0,recved=9523,sent=9523)
 /172.18.0.2:59490[1](queued=0,recved=1006,sent=1006)
 /172.18.0.2:59494[1](queued=0,recved=24283,sent=24283)
 /172.18.0.2:60686[1](queued=0,recved=502,sent=502)
 /172.18.0.2:33978[1](queued=0,recved=495,sent=495)
 /172.18.0.2:55896[1](queued=0,recved=1064,sent=1065)
 /172.18.0.2:58374[1](queued=0,recved=512,sent=512)
 /172.18.0.2:54034[1](queued=0,recved=1652,sent=1657)
 /172.18.0.2:58280[1](queued=0,recved=2321,sent=2347)
 /172.18.0.2:54030[1](queued=0,recved=1166,sent=1166)
 /172.18.0.2:33514[1](queued=0,recved=498,sent=498)

Latency min/avg/max: 0/3/4073
Received: 58753
Sent: 58797
Connections: 19
Outstanding: 0
Zxid: 0xe25
Mode: standalone
Node count: 318

[zookeeper@sandbox-hdp ~]$ echo wchc|nc localhost 2181
0x169670ccd570006
	/ambari-metrics-cluster/INSTANCES/sandbox-hdp.hortonworks.com_12001/MESSAGES
0x169670ccd570009
	/hbase-unsecure/master
	/hbase-unsecure/namespace/default
	/hbase-unsecure/namespace/hbase
	/hbase-unsecure/normalizer
	/hbase-unsecure/switch/merge
	/hbase-unsecure/rs/sandbox-hdp.hortonworks.com,16020,1552214703261
	/hbase-unsecure/namespace
	/hbase-unsecure/running
	/hbase-unsecure/balancer
	/hbase-unsecure/switch/split
0x169670ccd57000e
	/controller
	/isr_change_notification
	/admin/preferred_replica_election
	/admin/reassign_partitions
	/log_dir_event_notification
	/brokers/ids
	/admin/delete_topics
	/config/changes
	/brokers/topics/ATLAS_ENTITIES
	/brokers/topics/__consumer_offsets
	/brokers/topics
0x169670ccd570008
	/druid/listeners/lookups/__default/sandbox-hdp.hortonworks.com:8082
0x169670ccd570017
	/hiveserver2/serverUri=sandbox-hdp.hortonworks.com:10000;version=1.2.1000.2.6.5.0-292;sequence=0000000005
0x169670ccd570007
	/ambari-metrics-cluster/IDEALSTATES
	/ambari-metrics-cluster/CONFIGS/PARTICIPANT
	/ambari-metrics-cluster/LIVEINSTANCES/sandbox-hdp.hortonworks.com_12001
	/ambari-metrics-cluster/CONTROLLER
	/ambari-metrics-cluster/LIVEINSTANCES
	/ambari-metrics-cluster/CONTROLLER/MESSAGES
	/ambari-metrics-cluster/IDEALSTATES/METRIC_AGGREGATORS
	/ambari-metrics-cluster/CONFIGS/PARTICIPANT/sandbox-hdp.hortonworks.com_12001
	/ambari-metrics-cluster/INSTANCES/sandbox-hdp.hortonworks.com_12001/CURRENTSTATES/169670ccd570006
	/ambari-metrics-cluster/INSTANCES/sandbox-hdp.hortonworks.com_12001/CURRENTSTATES/169670ccd570006/METRIC_AGGREGATORS
	/ambari-metrics-cluster/INSTANCES/sandbox-hdp.hortonworks.com_12001/MESSAGES
0x169670ccd570015
	/hbase-unsecure/master
	/hbase-unsecure/rs/sandbox-hdp.hortonworks.com,16020,1552214703261
	/hbase-unsecure/running
	/hbase-unsecure/meta-region-server

If you got an error when using 4lw commands like this :

[zookeeper@sandbox-hdp ~]$ echo wchc|nc localhost 2181
wchc is not executed because it is not in the whitelist.

The reason is that in the last version for avoid security leaks and ddos attack on Zookeeper by using those 4lw you have to set a whitelist of the 4lw commands that could be used.

You could add in zoo.cfg the whitelist a comma list of 4lw commands or an * if you authorize all :

4lw.commands.whitelist=stat, ruok, conf, isro, wchc
or
4lw.commands.whitelist=*

Another security recommandation si to not expose the ZK servers ports at the outside of your cluster trusted network.