How we migrate production systems without downtime

Most migration failures are not technical. They come from an ambiguous cutover plan, an untested rollback and a team that finds out about the switch on the morning it happens.

We run every migration as blue/green. The new environment is built and load-tested in parallel with production, traffic is shifted in stages behind a proxy, and the old environment stays warm until the new one has held for a full business cycle.

The three checks that catch most problems: verify restores rather than backups, replay real production traffic before the switch, and write the rollback trigger as a number — not a judgement call.