No system is 100% reliable, though. Some systems are close enough that we grit our teeth and pretend they are and wave away the inevitable outages that have not

No system is 100% reliable, though. Some systems are close enough that we grit our teeth and pretend they are and wave away the inevitable outages that have nothing to do with our app and everything to do with an unreliable dependency. In a way, you're better off with a 99% reliable dependency than 99.9999%. If you expect it to be down some of the time, you'll plan for it in your architecture and (in theory) gracefully handle the failure whether it's due to an insufficiency warmed container, a network issue, a bad deploy, or whatever else comes along.