How we migrate production systems without downtime
The scariest sentence in IT is 'we'll just switch everything over on the weekend.' Production migrations fail not because the technology is hard, but because they're treated as an event instead of a process. Our runbook is boring on purpose β here's what's in it.
Parallel environments, not leaps
We build the new environment next to the old one and run both at once. Real traffic flows to the old system; mirrored traffic hits the new one. Differences show up in dashboards, not in customer complaints.
Rehearse the cutover
Before the real migration we run the entire cutover at least twice on staging β with a stopwatch. Every step is written down with an owner and a time budget. If a step has no rollback, it doesn't go in the plan.
A tested way back
The rollback plan is rehearsed too. Knowing you can return in ten minutes changes the psychology of the whole night: nobody makes panic decisions at 2 a.m., because there's nothing to panic about.
The boring result
Our record so far: a 24/7 dispatch system for a 300-vehicle fleet moved to new infrastructure with zero minutes of downtime. Nobody noticed β which was exactly the point.