Canary Deployment

Version 2 passed every test. But production has millions of users and behaviours your tests never reproduced. Sending everyone to v2 immediately is risky.

It's named after canaries once used in coal mines to warn miners of dangerous gases. Expose a small percentage first.

95% → v1
 5% → v2

Observe it, then gradually increase exposure. Blue-green is one way to support a canary rollout. Canary describes how you introduce traffic. Blue-green describes how you arrange the deployments. They can work together. Another option is to run a small group of new-version instances alongside old ones in the same environment and route a small share of traffic to them.