etcd

etcd is a strongly consistent, distributed key-value store designed for storing critical configuration data and providing distributed system coordination. Originally created at CoreOS (later acquired by Red Hat, which was in turn acquired by IBM) in 2013 by Xiang Li and the CoreOS team, etcd has become a foundational component of the cloud-native infrastructure, most notably serving as the backing store for all cluster state in Kubernetes. Every Kubernetes deployment relies on etcd to store the cluster's entire state, including pod definitions, service configurations, secrets, and cluster membership information. The name etcd comes from the Unix etc directory (where configuration files are stored) combined with the d suffix (for distributed). Key features include: a simple HTTP/gRPC API for reading and writing key-value pairs, range queries, and watching for changes, strong consistency guarantees via the Raft consensus algorithm (ensuring all nodes agree on the current state and can tolerate the loss of up to N/2 minus 1 nodes in a cluster of N nodes), support for transactions (atomic compare-and-swap operations for optimistic concurrency control), lease-based key expiration (keys can be associated with time-to-live leases that automatically delete the key when the lease expires, useful for service discovery and health checking), watch API for real-time notifications when keys change (enabling reactive configuration updates across distributed services), authentication and role-based access control (RBAC) for securing access to the key-value store, compact and snapshot-based data storage (periodically compacting the history of changes and creating point-in-time snapshots for efficient recovery and backup), TLS encryption for both client-server and peer-to-peer communication, and a maintenance API for defragmentation, snapshotting, and version management. As of 2026, etcd has over 48,000 GitHub stars.