"To me, this outage is the most worrisome of all AWS service disruptions that I know about. In a nutshell:

AWS effectively lost its control plane for entire region as a result of a failure within a single AZ. This was not supposed to be possible."

I find it funny how we have this assumption that if we don't architect across multiple AZs or regions we shouldn't be surprised when our service goes down because of an AWS failure, but that if we do, we're "pretty safe" -- and then Amazon itself experiences failure spanning AZs from a single-AZ failure.