Which key-value store is used to persist Kubernetes cluster data?

etcd is a consistent and highly-available key-value store that serves as the backing store for all cluster data in Kubernetes. All Kubernetes objects (Pod definitions, service accounts, etc.) are stored in etcd, making it a critical component for the cluster's state and operation.

Apache ZooKeeper is another distributed coordination service but is not used by default or as the primary data store for Kubernetes clusters.

ControlPlaneStore is not a recognized or standard key-value store or component name within the Kubernetes architecture.

Redis is an in-memory data structure store, often used as a database, cache, and message broker, but it is not the persistence layer for Kubernetes cluster state.