That's interesting but not what I expected when I read "reliability". I would have expected SLO metrics like uptime of the network or similar metrics that users

That's interesting but not what I expected when I read "reliability". I would have expected SLO metrics like uptime of the network or similar metrics that users would care about more. Usually when scaling a system that's built well you don't have hard short constraints on how fast an instance needs to be spun up. If you are unable to spin up any that can be problematic of course. Ideally this is all automated so nobody would care much about whether it takes a retry or 30s longer to create an instance. If this is important to you, you have other problems.