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.