Is it necessary to use Zookeeper in Hadoop Stack

Question

I am new to Hadoop as well as ZooKeeper. I can't understand the purpose of using ZooKeeper with Hadoop?

Answer 1

ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services. All of these kinds of services are used in some form or another by distributed applications.​

Whereas Hadoop develops open-source software for reliable, scalable, distributed computing. 

The purpose of Zookeeper is cluster management. This fits with the general philosophy of *nix of using smaller specialized components - so components of Hadoop that want clustering capabilities rely on Zookeeper for that rather than develop their own.