The pattern recommended by amazon themselves is to run stuff in multiple regions. Stuff never really breaks in an AZ, its almost always a region that goes down

The pattern recommended by amazon themselves is to run stuff in multiple regions. Stuff never really breaks in an AZ, its almost always a region that goes down. Some workloads can't be split, but they are pretty small, especially when you start getting to medium load levels (anything involving sharding.) Mostly then its down to cost.