Backend & systems·Deployment, release and rollback
you stand up a complete second environment on the new version and switch all traffic to it at once.
Blue-green deployment
Running two full environments and cutting traffic from the old to the new in one step, with the old kept warm for rollback. Rollback is a traffic switch, which is as fast as it gets. It doubles infrastructure for the duration and does not help with shared state: the database is still singular and still migrated.