Re: Ever heard of a UPS?
I think UPS failover (or supply failover in general) is a good case for DC power distribution instead of AC tbh. I often worry about the stability of our AC electricity grids.
I don't know if Amazon had DC or AC distribution in this case, but I'd place a bet that it was standard 50/60Hz AC.
The big problem with AC is that your sources all need to be in phase, so you can't easily have multiple UPSs holding up the same busbar. Normally you end up with one big inverter somewhere, which is a single point of failure.
You can still have smaller UPSs on individual servers though, and you can have redundant PSUs inside the servers themselves which use diodes as a failover mechanism. But you can only do that after it has been rectified to DC.
Any 'mission-critical' server like a disk array would "shurley" have double, if not triple redundant PSUs with separate AC busbars and separate UPSs though, so I'd be surprised if this outage was just a UPS failure. If so then some IT/electrical engineering heads could roll at Amazon.
Biting the hand that feeds IT
