ZooKeeper Client Tutorial

ZooKeeper is a distributed configuration and synchronization service for large distributed systems. ZooKeeper's architecture supports high availability through redundant services. In the following tutorial we are going to start a group of ZooKeeper servers, then interact with them from both the command line and a GUI client. First download the zip file which contains everything you need:

Download ZooKeeper Demo

ZooKeeper Tutorial

ZooKeeper Architecture

First it would be best to introduce what ZooKeeper is. ZooKeeper is a replicated service spread over a number of servers called an ensemble. It provides a set of reliable basic services, similar to a filesystem to allow coordination. It's architecture looks like this:

ZooKeeper nodes store their data in a hierarchical name space, much like a file system or a tree data structure. Clients can read from and write to the nodes and in this way have a shared configuration service. Updates are totally ordered.

Run ZooKeeper Servers

First download the demo files. Once unzipped you will see it has a number of folders s1/s2/s3 that contains the config for three servers and a number of .bat files for launching. To run a single server we could specify the command: java -jar ../zookeeper-3.3.3-fatjar.jar server s.cfg within the .cfg file is the config which looks like this:

We are going to run three servers to demonstrate failover, to do this use start-servers.bat. These three servers run based on config in directories s1/s2/s3 respectively like so:

Start a Client and connect to server

To start a client that will connect to our servers we can either run start-client.bat or the command java -jar zookeeper-3.3.3-fatjar.jar client -server. Below you can see me starting a command line client and then using the ls and create commands. I use create /demo1 "example of zk" to create a new node demo1 with some string data:

ZooKeeper GUI Client

To start the zooinspector client run javaw -cp * org.apache.zookeeper.inspector.ZooInspector:

Create/Watch/Delete zNodes

Some Commands available in the cli client include:

ZooKeeper Command Line Commands

Command Description
help Display possible commands
ls path [watch] List the contents of a zNode and optionally watch it for changes.
create path data Create a new zNode containing the data specified.
set path data Set the data for an existing zNode.
delete path Delete an existing path.