Blue-Green Deployment

Blue-green deployment is a release technique that runs two identical production environments. The "blue" environment serves live users while the new version is deployed and tested in the "green" environment; when it is ready, traffic is switched to green in one step, usually at the load balancer.

If something goes wrong, traffic is switched back to blue instantly, giving near-zero downtime and an easy rollback. Related techniques include canary deployment, which sends a small percentage of users to the new version first, and rolling deployment, which replaces servers one batch at a time.