Flow
- The green environment is updated to the new version
- Smoke tests run on green
- The load balancer switches all traffic from blue to green
- Blue stays on standby — rollback takes seconds
Advantages
- Zero downtime — switching is instantaneous
- Easy rollback — just switch traffic back
- Smoke testing on real infrastructure before users see it
Alternatives
Canary deployment — gradual rollout (1% → 10% → 100%). Rolling deployment — updating instances one at a time without stopping traffic.