2.2.1 Blue-Green Deployments
Blue is live. You deploy green, test it, then flip the balancer. Roll back by flipping back.
Why it matters
Users never sit on a half-migrated fleet. Rollback is instant if schemas are compatible.
How it is used
Keep both stacks sized for full load (cost). Schema changes must work with both binaries during the flip. Drain connections before shutting blue down.