Kubernetes stores all of its cluster state in etcd, a distributed data store with a strong consistency model. etcd is a distributed, reliable key-value store for the most critical data of a distributed system, with a focus on being:
- Simple: Well-defined, user-facing API
- Secure: Automatic TLS with optional client cert authentication
- Fast: Benchmarked for 10,000 writes/sec
- Reliable: Properly distributed using Raft
This state includes what nodes exist in the cluster, what Pods should be running, which nodes they are running on, and a whole lot more. The whole cluster state is stored in an instance of etcd. This provides a way to store configuration data reliably. Another crucial component running on the Master node is the API server. ...