[threeseed]

High availability is more important than scalability for most.

On average an AWS availability zone tends to suffer at least one failure a year. Some are disclosed. Many are not. And so that database you are running on a single instance will die.

Question is do you want to do something about it or just suffer the outage.

[riku_iki]

I think major providers provide PG service with cross zone availability through replication.