Ratis

Apache Ratis is a highly customizable open-source Java implementation of the Raft consensus protocol. Raft is an easily understandable consensus algorithm designed to manage replicated state. Unlike ZooKeeper or other Raft implementations such as etcd, Ratis is designed as a library rather than a standalone consensus server, which simplifies its management and integration.

Ozone leverages Ratis to replicate system states across multiple nodes, ensuring high availability and redundancy. When using Ratis for replication, each piece of data written by clients is replicated to 3 Datanodes. Within Ozone, Ratis is employed in critical components such as the Ozone Manager, Storage Container Manager, and Datanodes. It forms the central pillar for the High Availability (HA) mechanisms of both the Ozone Manager (OM-HA) and Storage Container Manager (SCM-HA).

For more detailed information, please visit the Apache Ratis website.