Lesson 16 / 21

Canary Releases

Ship to a small slice of traffic first, and watch before widening.

How it works

Route a small percentage of real traffic (say 5%) to the new version while the rest keeps hitting the old one. If metrics stay healthy, gradually increase the percentage until it's 100%.

Canary in a coal mine

Miners once carried a canary into the tunnel — if it stopped singing, they knew danger was present before it reached them. A canary release exposes the new version to a small group first, as an early-warning signal.

Watch the right metrics

Error rate, latency, and business metrics (checkout success) on the canary slice — not just 'is it up'. Widen only when those numbers match or beat the baseline.