Etcd

https://coreos.com/using-coreos/etcd/

etcd is an open-source distributed key value store that provides the backbone of CoreOS clusters and the etcd client runs on each machine in a cluster. etcd gracefully handles master election during network partitions and the loss of the current master.

Your applications can read and write data into etcd. Common examples are storing database connection details, cache settings, feature flags, and more. Features


 * Simple, curl-able API (HTTP + JSON)
 * Optional SSL client cert authentication
 * Benchmarked 1000s of writes/s per instance
 * Properly distributed using Raft protocol
 * Keys support TTL
 * Atomic test and set
 * Easily listen for changes to a prefix via HTTP long-polling

Related: CoreOS