There is a tale - perhaps apocryphal - handed down between generations of AWS staff, of a customer that was all-in on spot instances, until one day the price and availability of their preferred instances took an unfortunate turn, which is to say, all their stuff went away, including most dramatically the customer data that was on the instance storages, and including the replicas that had been mistakenly presumed a backstop against instance loss, and sadly - but not surprisingly - this was pretty much terminal for their startup.
Caveat operator.
(I’m sure parent commenter is either not exposed to this scenario or has otherwise mitigated against it)
We've worked closely with our team at AWS to ensure we are following best practices. The consensus has been that 4+ AZs and 12 instance types is sufficient diversification.
We also have a second, on demand, ASG ready to fire up at a moments notice if something were to happen with capacity.
We also heavily leverage managed services for state.
Caveat operator.
(I’m sure parent commenter is either not exposed to this scenario or has otherwise mitigated against it)