Blue-Green vs Canary Deployments

Blue-green and canary are two deployment strategies that reduce the risk of releasing new versions. Blue-green maintains two identical environments and switches traffic between them. Canary gradually routes a small percentage of traffic to the new version before rolling out fully.

Blue-Green Deployments

Two identical environments run in parallel: blue (current production) and green (new version). You deploy the new version to green, verify it works, then switch the load balancer to direct all traffic to green. If something goes wrong, switch back to blue immediately.

The biggest advantage is rollback speed — it is literally a load balancer configuration change. The biggest drawback is cost — you maintain double infrastructure.

Canary Deployments

You deploy the new version to a small subset of instances (the "canary"). A traffic router sends 1-5% of production traffic to the canary while monitoring error rates, latency, and business metrics. If metrics look good, gradually increase the percentage until 100% of traffic hits the new version.

This approach catches issues early with minimal user impact. If the canary shows elevated errors, roll back before most users are affected.

The Database Problem

Both strategies struggle with database schema changes. If the new version requires schema changes, you need backward-compatible migrations that work with both old and new application versions simultaneously.

For deployment best practices, see our concepts library and system design interview guide. Check pricing for access.

The Bottom Line

Use blue-green for simple, fast rollback with acceptable infrastructure cost. Use canary for risk-sensitive production environments where gradual validation with real traffic is worth the monitoring investment.