etcd

etcd is a distributed key-value store that keeps critical data reliable across a cluster of machines. It is a CNCF project, and it is designed for systems where many machines must agree on the same data.

etcd stores values under a hierarchy of keys, similar to directories in a file system. Clients read and write with standard HTTP tools, and they can watch keys or directories for changes. It uses the Raft protocol, so it can elect a new leader when a network partition or machine failure happens.

• Simple HTTP read and write interface
• Hierarchical key storage
• Watch keys or directories for changes
• Optional TTLs for expiring keys
• Optional SSL client certificate authentication

Platform engineers and developers who build distributed systems that need a shared store for configuration, coordination or feature flags. Teams that run clusters and need one consistent source of truth may also use it.

etcd is open source under the Apache 2.0 licence and free to use. The main costs are the machines it runs on and the work of operating a cluster. It is meant for critical coordination data rather than bulk storage, so check that the fit is right before using it for large data sets.