Backend & systems·Deployment, release and rollback
the deploy broke something so you put the previous version back rather than trying to fix forward under pressure.
Rollback
Returning to the previously known-good version. It is the correct default response to a bad deploy, and its speed is a top-tier reliability metric. It is only available if every change is backward compatible with the previous version's data — an unrecoverable migration makes rollback impossible exactly when you need it.