Blue-green deployment
Also called Blue-green
Two identical production environments. One serves users while you deploy to the other and check it. Then you switch the traffic across, and the old one stays ready to switch back to.
Going back becomes flipping a switch, and nobody meets a half-finished deploy. You pay for two environments while you keep both, and there is usually one database, which both versions have to work with.
Say it to your agent
“Deploy to the idle environment and run the smoke tests on its private URL. Only then switch the load balancer, and keep the old one running for an hour. Any database change has to work with both versions, so do that first, separately.”