Blue-Green Deployment
Running two identical production environments and switching traffic from the old one to the new one in a single cut, with the old kept warm for rollback.
Deploy to the idle environment, verify it, then flip the router. Rollback is flipping back, which takes seconds and requires no rebuild — that is the whole value proposition.
Two constraints decide whether it is practical. Cost: you are running double capacity during
the overlap. Database schema: both versions may briefly serve traffic against the same
database, so every schema change must be backward compatible — which means expand-and-contract,
not an in-place ALTER. Teams that skip this discover that the rollback path they were paying for
does not actually work.
Compare with canary release, which shifts a small percentage of traffic gradually and gives you real-user signal before full exposure. Canary is usually the better default; blue-green is simpler and suits systems where partial rollout is not meaningful.