alt Hacker NewsI was surprised hitting one of these limits once, but it wasn't as if they were 100% out of servers, just had to pick a different node type. I don't think they would ever post their numbers, but some of the more exotic types definitely have less in the pool.
If you work at AWS in a technical role you can check the capacity of each pool in each AZ using an internal tool. Previously the main reason for pool exhaustion was automated jobs at the start of each working day as well as instance slotting issues (releasing a 4xl but only re-allocating a l means you now cannot slot another 4xl).