ZooKeeper

ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services

Resources

• Documentation

• Curator

Setup

Requirements

• Base image

Build devops/zookeeper image

# change path
cd devops/zookeeper

# build image
docker build -t devops/zookeeper:latest .
# build image with specific version - see Dockerfile for version 3.5.x
docker build -t devops/zookeeper:3.4.10 --build-arg VERSION=3.4.10 .

# temporary container [host:container]
docker run --rm --name zookeeper -p 12181:2181 devops/zookeeper
# access container
docker exec -it zookeeper bash

# paths
/opt/zookeeper
/var/log/zookeeper
/var/lib/zookeeper
/var/log/supervisord.log

# logs
tail -F /var/log/supervisord.log
# check service status
supervisorctl status
supervisorctl restart zookeeper

Example

docker exec -it zookeeper bash

# (option 1) check zookeeper status
echo ruok | nc localhost 2181

# (option 2) check zookeeper status
telnet localhost 2181
# expect answer imok
> ruok

zkCli.sh -server 127.0.0.1:2181
help
# list znodes
ls /
# create znode and associate value
create /zk_test my_data
# verify data
get /zk_test
# change value
set /zk_test junk
# delete znode
delete /zk_test

The four-letter words

Category	Command	Description
Server status	ruok	Prints imok if the server is running and not in an error state
	conf	Prints the server configuration (from zoo.cfg)
	envi	Prints the server environment, including ZooKeeper version, Java version, and other system properties
	srvr	Prints server statistics, including latency statistics, the number of znodes, and the server mode (standalone, leader, or follower)
	stat	Prints server statistics and connected clients
	srst	Resets server statistics
	isro	Shows whether the server is in read-only ( ro ) mode (due to a network partition) or read/write mode (rw)
Client connections	dump	Lists all the sessions and ephemeral znodes for the ensemble. You must connect to the leader (see srvr) for this command
	cons	Lists connection statistics for all the server's clients
	crst	Resets connection statistics
Watches	wchs	Lists summary information for the server's watches
	wchc	Lists all the server's watches by connection, may impact server performance for a large number of watches
	wchp	Lists all the server’s watches by znode path, may impact server performance for a large number of watches
Monitoring	mntr	Lists server statistics in Java properties format, suitable as a source for monitoring systems such as Ganglia and Nagios