etcd

The distributed key-value store that serves as the consistent backbone for Kubernetes cluster state and service discovery.

Etcd is a strongly consistent, distributed registry built on the Raft consensus algorithm. It manages the critical state of large-scale systems (like Kubernetes) by ensuring every write is replicated across a majority of nodes before confirmation. Operators rely on its gRPC-based API and watchable key ranges to trigger immediate system reactions to configuration changes. Whether you are storing metadata for a 1,000-node cluster or managing leader election for a custom microservice, etcd provides the linearizable consistency required to prevent split-brain scenarios.

https://etcd.io