yeah, AWS rarely has significant capacity issues. While the capacity utilization typically sits around 90% across the board, they're constantly landing new capacity, recovering broken capacity, and working to fix issues that cause things to get stuck (and lots of alarms and monitoring).

I worked there for just shy of 7 years and dealt with capacity tangentially (knew a good chunk of their team for a while and had to interact with them frequently) across both teams I worked on (support and then inside the EC2 org).

Capacity, while their methodologies for expanding were, in my opinion, antiquated and unenlightened for a long time, were still rather effective. I'm pretty sure that's why they never updated their algorithm for increasing capacity to be more JIT. Now, they have a LOT more flexibility in capacity now that they have resource vectoring, because you no longer have hosts with fixed instance sizes for the entire host (homogenous). You now have the ability to fit everything like legos as long as it is the same family (ie. c4 with c4, m4 with m4, etc.) and there was additional work being done to have cross-family resource vectoring as well that was in-use.

Resource vectors took a LONG time for them to get in place and when they did, capacity problems basically went away.

The old way of doing it was if you wanted to have more capacity for, say, c4.xlarge, you'd either have to drop new capacity and build it out to where the entire host had ONLY c4.xlarge OR you would have to rebuild excess capacity within the c4 family in that zone (or even down to the datacenter-level) to be specifically built-out as c4.xlarge.

Resource vectors changed all that. DRAMATICALLY. Also, to reconfigure a hosts recipe now takes minutes, rather than rebuilding a host and needing hours. So, capacity is infinitely more fungible than it was when I started there.

Also, I think resource vectoring came on the scene around 2019 or so? I don't think it was there in 2018 when I went to work for EC2...but it was there for a few years before I quit...and I think it was in-use before the pandemic...so, 2019 sounds about right.

Prior to that, though, capacity was a much more serious issue and much more constrained on certain instance types.