Introduction to ZooKeeper: Concepts, Node Types, and Basic Installation

ZooKeeper is an open‑source, high‑performance coordination service designed for distributed applications, offering simple interfaces for naming, configuration management, synchronization, and group management, which helps developers avoid building these features from scratch.

It maintains an in‑memory hierarchical data model similar to a file system, where each node (znode) can store small pieces of data such as configuration or status information.

The four znode types are:

PERSISTENT : a regular node that remains after the client disconnects.

PERSISTENT_SEQUENTIAL : a persistent node whose name receives a sequential number assigned by ZooKeeper.

EPHEMERAL : a temporary node that is deleted when the client disconnects and cannot have children.

EPHEMERAL_SEQUENTIAL : a temporary sequential node that is removed on client disconnect, with ZooKeeper adding a sequential suffix to its name.

ZooKeeper also supports a watch mechanism, allowing clients to monitor a znode for data changes; when a change occurs, ZooKeeper notifies the client, similar to the observer pattern.

Before installing, ensure Java is installed on the machine. Upload the ZooKeeper package (e.g., version 3.8.3) to /usr/local , extract it, rename the sample configuration, and start the server:

tar -zxvf apache-zookeeper-3.8.3-bin.tar.gz
cd apache-zookeeper-3.8.3-bin
cp conf/zoo_sample.cfg conf/zoo.cfg
bin/zkServer.sh start

Verify the service with the ZooKeeper client:

bin/zkCli.sh

Running ls / shows the root nodes. Create a new node with create /fullstack followit , then list again to see the new node. Use get -s /fullstack to view its details.

This introductory guide covers the basic concepts and installation of ZooKeeper; future articles will explore clustering, leader election, and code examples.