Does Amazon rent out the servers that it doesn't use (say, in the spring) for AWS? If so, are AWS resources limited in the winter, when Amazon has a high load? If resources are not more limited, how does Amazon cope with both resources?
(Unless it simply has even MORE servers, so that it can support both everyone using AWS and everyone shopping for their Christmas GPUs.)
I'm assuming it's probably more likely to be the latter, where they also scale up using the same resources. This would be made possible because they always 'overprovision'. There aren't some exact number of servers they keep so that they are always running. In the case that some people are renting more often on a certain day of the month or something, obviously, they need to keep up with this.
Maybe they also have their own dedicated servers, could be a mix of both.
A good quora post on EC2: