etcd
etcd is a distributed, strongly consistent key-value store used for configuration,
service discovery, and coordination. It is the backing store for the
Kubernetes control plane — the API server persists all cluster state
(pods, services, secrets, and more) in etcd. Clients connect on port
2379; cluster members replicate data via the Raft consensus protocol.
Practice scenarios
Hands-on etcd scenarios on live Linux VMs: etcd