etcd

etcd is a strongly consistent, distributed key-value store that provides a reliable way to store data that needs to be accessed by a distributed system or cluster of machines. It gracefully handles leader elections during network partitions and can tolerate machine failure, even in the leader node. Learn more
Read and write values using standard HTTP tools, such as curl
Store data in hierarchically organized directories, as in a standard filesystem
Watch specific keys or directories for changes and react to changes in values
Optional SSL client certificate authentication
Benchmarked at 1000s of writes/s per instance
Optional TTLs for keys expiration
Properly distributed via Raft protocol