blue-green deployment

Blue-green deployment maintains two production environments, switching traffic between them for zero-downtime updates. **Setup**: Blue environment runs current production. Green environment gets new version. Switch traffic to green when ready. Blue becomes standby. **Deployment process**: Deploy new model to idle environment (green), run validation, switch traffic to green, monitor. Blue available for instant rollback. **Advantages**: Zero downtime, instant rollback (switch back to blue), full testing in production-like environment before traffic switch. **Traffic switching**: DNS change, load balancer update, or router configuration. Should be fast and atomic. **Rollback**: Simply route traffic back to blue. Previous version still running and warm. **Resource cost**: Two complete environments - double infrastructure (though one is idle). **Comparison to canary**: Blue-green is all-or-nothing switch. Canary is gradual. Can combine: canary within green environment. **Model serving application**: Have two model deployments, switch load balancer target. Keep old model loaded for quick rollback. **Best practice**: Ensure both environments identically configured, automate switching, test rollback procedure.