Moving day, without closing the shop

Every update, and every move between the shared building and a house of its own, happens while the site keeps serving visitors. Engineers call it a blue/green deploy: a new copy of the site starts next to the old one, and only when it's healthy does the front door start sending people to it. Two details make it truly seamless. The caretaker doesn't assume the front door has switched over, it checks the front door's own numbers until it has. And the old copy is told to "drain" first: it stops accepting new visitors, finishes whatever it was doing, and only then switches off.