etcd — Distributed Reliable Key-Value Store for Critical Data

What it is

etcd is an open-source, strongly consistent, distributed key-value store written in Go. It uses the Raft consensus algorithm to ensure data reliability across a cluster of machines. etcd is the backbone of Kubernetes, storing all cluster state, configuration, and metadata.

Beyond Kubernetes, etcd serves as a building block for service discovery, distributed locking, leader election, and configuration management in any distributed system that needs a reliable source of truth.

How it saves time or tokens

Building a distributed consensus system from scratch is a multi-year effort. etcd provides a battle-tested implementation of Raft with a simple key-value API. Teams adopt etcd instead of implementing their own coordination layer, saving months of engineering. Its watch API enables reactive architectures where services respond to configuration changes instantly rather than polling.

How to use

1. Download the etcd binary from the official releases page or install via your package manager.
2. Start a single-node cluster for development with etcd (no flags needed) or configure a multi-node cluster with peer URLs.
3. Use etcdctl to read and write keys: etcdctl put mykey myvalue and etcdctl get mykey.

Example

# Start etcd locally
etcd --listen-client-urls http://localhost:2379 \
     --advertise-client-urls http://localhost:2379

# Put and get a key
etcdctl put /config/db_host '192.168.1.100'
etcdctl get /config/db_host
# Output: /config/db_host
# 192.168.1.100

# Watch for changes
etcdctl watch /config/ --prefix

Related on TokRepo

• DevOps tools — Infrastructure and deployment automation
• Self-hosted solutions — Run critical services on your own infrastructure

Common pitfalls

• etcd is not a general-purpose database. It is designed for small amounts of critical metadata (default max value size is 1.5MB). Do not store large blobs or high-volume transactional data.
• Cluster sizing matters. A 3-node cluster tolerates 1 failure, a 5-node cluster tolerates 2. Always run an odd number of nodes.
• Disk I/O latency directly affects etcd performance. Use SSDs for the data directory. Slow disks cause leader election timeouts and cluster instability.