Blue-Green Deployments#

A blue-green deployment runs two identical production environments. One (blue) serves live traffic. The other (green) is idle or running the new version. When the green environment passes validation, you switch traffic from blue to green. If something goes wrong, you switch back. The old environment stays running until you are confident the new version is stable.

The fundamental advantage over rolling updates is atomicity. Traffic switches from 100% old to 100% new in a single operation. There is no period where some users see the old version and others see the new one.