etcd

etcd is a distributed, reliable key-value store written in Go. It uses the Raft consensus algorithm to keep a strongly-consistent, replicated log across cluster members, and exposes a gRPC API (with an HTTP/JSON gateway) for clients. The repository hosts the server, the official Go client, the etcdctl and etcdutl command-line tools, the gRPC proxy, the watch cache, integration / robustness test suites, and a collection of internal tools.

What is in this wiki

• Architecture — how the binaries fit together at runtime.
• Getting started — clone, build, run, and exercise a local etcd cluster.
• Glossary — etcd vocabulary you will see across the code (revision, lease, learner, MVCC, WAL...).
• How to contribute — workflow, testing, debugging, and conventions.
• Applications — etcd, etcdctl, and etcdutl binaries.
• Modules — workspace layout (api/, client/, server/, pkg/, cache/, tests/, tools/, ...).
• Systems — internal subsystems like raft transport, MVCC, WAL, leases, auth.
• Features — cross-cutting capabilities such as watch, transactions, snapshots, and learners.
• API — gRPC services and protobuf surface.
• Deployment and Security — operational and threat-model notes.
• Monitoring — logging, metrics, and tracing.
• Reference — configuration, data models, dependencies.

Repository at a glance

Item	Value
Primary language	Go
Go workspace modules	11 (./, api, cache, client/pkg, client/v3, etcdctl, etcdutl, pkg, server, tests, tools/...) — see go.work
Source files (Go)	~1,100
Lines of Go	~246,000
First commit	2013‑06‑06
Latest commit at wiki time	28af95a2d (2026‑04‑29)
License	Apache 2.0 (LICENSE)
Governance	CNCF graduated project (GOVERNANCE.md, OWNERS)

Where the entry points live

• main.go — top-level wrapper that calls etcdmain.Main so go install go.etcd.io/etcd@… still works.
• server/main.go — the actual server module entry point.
• server/etcdmain/etcd.go — flag parsing and bootstrap logic; chooses between etcd server, gateway, and grpc-proxy modes.
• server/embed/etcd.go — embed.Etcd, the library form used by the binary and by other Go projects that embed etcd.
• etcdctl/main.go — calls ctlv3.MustStart; the v3 client CLI.
• etcdutl/main.go — offline data-file utility; backups, snapshots, WAL surgery.

Useful external links

• Project site: https://etcd.io
• API reference: https://etcd.io/docs/latest/learning/api
• Operating guide: https://etcd.io/docs/latest/op-guide
• Robustness testing: tests/robustness/README.md
• CNCF page: https://www.cncf.io/projects/etcd