Zero-Downtime Deployment

Zero-downtime deployment means putting a new version of your system live while people carry on using it. No sign on the door. No message saying the service is closed for maintenance this evening. The shop keeps selling and the clinic keeps booking while the update happens underneath.

The old way was to pick a quiet hour, switch everything off, copy the new files up and hope. If something broke at eleven at night, somebody was awake fixing it. For a small internal tool that is still fine. For anything a customer touches it costs real orders, and a fair amount of patience you will not get back.

The modern way is simpler than it sounds. A second copy of the system is started with the new version on it. Users are then moved across to it a few at a time, while the old copy keeps running. If the new one behaves, everybody is on it within minutes. If it does not, everyone goes back to the old copy and almost nobody notices. That last step is the whole point, and it is the one to insist on.

Releasing to a few people first has another benefit. Give the new version to five of your own staff before you give it to five thousand customers. They will find the awkward screen within the hour. Linkysoft normally releases to the client's own team for a day, then to everyone, because a real user finds things no test finds.

Three things belong in the support agreement, in writing. That updates go out without closing the service. How fast the supplier can put the previous version back, say fifteen minutes, and who makes that call. And what happens to the database, because a change to the way data is stored is the part that cannot always be undone in a hurry. A supplier who answers those three clearly has done this before. Linkysoft builds the way back into every web application project it takes on, so an update can be taken away without rebuilding anything, and it is why Hostrena keeps a second copy of a site ready rather than one. The second copy costs a little. A closed evening costs more.