Apache ZooKeeper is an open-source server for highly reliable distributed coordination of cloud applications.

[4] ZooKeeper is used by companies including Yelp, Rackspace, Yahoo!,[5] Odnoklassniki, Reddit,[6] NetApp SolidFire,[7] Meta,[8] Twitter[9] and eBay as well as open source enterprise search systems like Solr and distributed database systems like Apache Pinot.

for streamlining the processes running on big-data clusters by storing the status in local log files on the ZooKeeper servers.

ZooKeeper was developed in order to fix the bugs that occurred while deploying distributed big-data applications.

Some of the prime features of Apache ZooKeeper are: Some common terminologies regarding the ZooKeeper architecture: The services in the cluster are replicated and stored on a set of servers (called an "ensemble"), each of which maintains an in-memory database containing the entire data tree of state as well as a transaction log and snapshots stored persistently.