What It Actually Takes to Network a Live System That's Never Allowed to Go Offline
There is a version of network engineering where you get a maintenance window. Somebody sends a calendar invite, everyone agrees that Sunday 2 a.m. to 6 a.m. belongs to you, and if you overrun by twenty minutes the worst thing that happens is an apologetic email.
I have spent more than a decade doing the other version. The systems I build carry video surveillance, public address, intercom, and emergency two-way communication for a large public transit network. The stations stay open. Trains keep running underneath the work. There is no window where the system is allowed to be down, because "down" means a passenger presses a call button in an elevator and nobody answers.
That single constraint reshapes every technical decision that follows. I want to walk through what it actually changes, because I think a lot of the network design advice floating around assumes a greenfield that most infrastructure...
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