This document defines the various terms used in etcd documentation, command line and source code.

Alarm

The etcd server raises an alarm whenever the cluster needs operator intervention to remain reliable.

Authentication

Authentication manages user access permissions for etcd resources.

Client

A client connects to the etcd cluster to issue service requests such as fetching key-value pairs, writing data, or watching for updates.

Cluster

Cluster consists of several members.

The node in each member follows raft consensus protocol to replicate logs. Cluster receives proposals from members, commits them and apply to local store.

Compaction

Compaction discards all etcd event history and superseded keys prior to a given revision. It is used to reclaim storage space in the etcd backend database.

Election

The etcd cluster holds elections among its members to choose a leader as part of the raft consensus protocol.

Endpoint

A URL pointing to an etcd service or resource.

Key

A user-defined identifier for storing and retrieving user-defined values in etcd.

Key range

A set of keys containing either an individual key, a lexical interval for all x such that a < x <= b, or all keys greater than a given key.

Keyspace

The set of all keys in an etcd cluster.

Lease

A short-lived renewable contract that deletes keys associated with it on its expiry.

Member

A logical etcd server that participates in serving an etcd cluster.

Modification Revision

The first revision to hold the last write to a given key.

Peer

Peer is another member of the same cluster.

Proposal

A proposal is a request (for example a write request, a configuration change request) that needs to go through raft protocol.

Quorum

The number of active members needed for consensus to modify the cluster state. etcd requires a member majority to reach quorum.

Revision

A 64-bit cluster-wide counter that is incremented each time the keyspace is modified.

Role

A unit of permissions over a set of key ranges which may be granted to a set of users for access control.

Snapshot

A point-in-time backup of the etcd cluster state.

Store

The physical storage backing the cluster keyspace.

Transaction

An atomically executed set of operations. All modified keys in a transaction share the same modification revision.

Key Version

The number of writes to a key since it was created, starting at 1. The version of a nonexistent or deleted key is 0.

Watcher

A client opens a watcher to observe updates on a given key range.