Apache ZooKeeper

Developer(s)	Apache Software Foundation
Stable release	3.4.9 / September 3, 2016 (2016-09-03)
Repository	github.com/apache/zookeeper
Written in	Java
Operating system	Cross-platform
Type	Distributed computing
License	Apache License 2.0
Website	zookeeper.apache.org

Apache ZooKeeper is a software project of the Apache Software Foundation. It is essentially a distributed hierarchical key-value store, which is used to provide a distributed configuration service, synchronization service, and naming registry for large distributed systems. ZooKeeper was a sub-project of Hadoop but is now a top-level project in its own right.

ZooKeeper's architecture supports high availability through redundant services. The clients can thus ask another ZooKeeper leader if the first fails to answer. 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.

ZooKeeper is used by companies including Rackspace, Yahoo!, Odnoklassniki, Reddit and eBay as well as open source enterprise search systems like Solr.

Typical use cases

• Naming service
• Configuration management
• Synchronization
• Leader election
• Message Queue
• Notification system

See also

• Hadoop

External links

• Official website
• Article in highscalability.com
• Software Development Times article of ZooKeeper moving to Apache
• Eclipse ECF Discovery based on Apache ZooKeeper