Twitter runs their own data centers, which means they own all of the THOUSANDS of machines in them. These machines, and all of their parts, have shelf lives and CONSTANTLY need replacement.
When they are replaced you can't just go to Best Buy with a credit card. At scale VERY SMALL changes matter: oh look they changed something in the disk firmware and haha now your databases corrupt data one out of 1M writes.
New machines need to be tested, burned in, installed. Old ones need to be cycled out.
Same goes for power equipment, networking, all that.
Because you built your own data center, and you were an early scale company it ALSO means a huge percentage of your systems are home grown - asset management, deployment, health checking, metrics, you name it. There are no articles on Stack Overflow. There is no blog post. How that shit works is mostly a function of what people knew about it and, well, at least half of those people are now poof - gone.
This hasn't even gotten to the services themselves, many of which are now running without an owner or any person at the company who has ever looked at them before. The remaining people are now up to their eyeballs in drama, survivor syndrome, fear, and, oh yeah, the work of many of their laid-off peers.
Few people, pfft, give me a break.
Also software engineers: be sure not to fire Ned or else the whole bridge might collapse
So your patient might be ok if you fire Ned, but if you try to make changes and a critical system goes down, it might take you a lot longer to fix things without the specialists in that system.
You could keep one specialist around for each system, but then you have a very small bus factor.
Look at all the other major engineering failures in history, it’s always small things (a gasket) on a bad day (too cold?) that somehow works day after day until one day it magically doesn’t and you get the Apollo incident. Everything goes catastrophic over tiny things. Imagine if NASA fired half their team before that incident. The only guy who knew the gasket can’t get cold might not still be there because Ned got laid off.
Software engineers: We did document he was a load-bearing Ned. He was Ops, of course he doesn't code regularly.
Even if you can refactor and simply their work to half the workload, you can’t do that within a week. Even the boring organizational stuff is crazy at this scale. They for sure slashed whole teams at once. Who turned off those services? Or if they’re meant to be running, who owns them, organizationally? Where is the code living, what repo, what part of the code base, when something goes wrong, what metrics are being watched? Overnight teams had to become responsible for twice the code/services, potentially stuff they have never seen before. Bloated or not, that’s not easy.
