How to implement blue-green deployments

Short answer

Maintain two identical environments: "blue" (live) and "green" (idle). Deploy the new version to green, run smoke tests, then route traffic from blue to green. Keep blue available for instant rollback.

Details

Blue-green deployments eliminate downtime because the load balancer switches traffic atomically rather than replacing running instances. The main cost is infrastructure overhead: you need double the compute capacity, though it can be temporary if you tear down the old environment after validation.

This strategy works best with stateless applications and shared databases that are backward-compatible. For containerized apps, a load balancer or ingress controller handles the switch. If you are orchestrating with Docker, see how to connect containers with user-defined networks for routing patterns.

Tips

• Run database migrations before the switch and ensure they are backward-compatible.
• Use health checks to confirm green is ready before cutting over traffic.
• For a related progressive rollout technique, read How to implement canary releases.