ZooKeeper, while being a coordination service for distributed systems, is a distributed application on its own. A collection of ZooKeeper servers forms a ZooKeeper ensemble. A quorum is represented by a strict majority of nodes in a ZooKeeper ensemble...
For reliable ZooKeeper service, you should deploy ZooKeeper in a cluster known as an ensemble. As long as a majority of the ensemble are up, the service will be available. Because Zookeeper requires a majority, it is best to use an odd number of machines...
