Blue-Green vs Canary Deployment
Instant environment swap versus gradual traffic shifting for zero-downtime releases.
Overview
What is being compared
Both are zero-downtime release strategies. Blue-green keeps two identical environments, deploys to the inactive one and switches traffic atomically. Canary shifts a small percentage of traffic to the new version and watches for errors before the full rollout.
- Traffic switch — All at once, at the load balancer — Gradual, 5% to 25% to 50% to 100%
- Main strength — Instant rollback — Limits blast radius during rollout
- Infrastructure — Double, both environments run until the switch — Only the capacity for the small initial share
- Rollback — Flip traffic back to the old environment — Shift traffic back to the old version, needs automation
- Old and new together — Yes, against the same database — Yes, against the same database
Traffic over time
Blue-green moves all traffic in one step; a canary moves it in stages. Each cell is the share of traffic on the new version: grey is none, yellow is a partial share, green is all of it.
A canary step only advances when the metrics hold; otherwise traffic goes back to the old version.
> [!IMPORTANT] Both strategies run old and new code against the same database, so schema changes must be backward-compatible (expand-contract).
> [!TIP] Both traffic models side by side, a canary rollout's steps and its automatic rollback, and the choice between the two play step by step in Visual Explanation below.
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