Amazon Availability Zones are such a fucking lie. ("Shared nothing, and an outage affecting one will not affect other Zones in the Region.")
I've seen more failures which take out multiple AZs than which take out only a single AZ. So, a prudent person would split their application across regions (which are relatively shared nothing, except for admin/account level stuff), but Amazon goes out of its way to not make that easy -- you're using the public Internet, pay higher costs, etc.
The right choice is probably EC2 plus a non-EC2 provider (your own hosted stuff, another cloud (?), etc.), with protection in case either goes down. But that is a relatively lot of work, and if you're on a PaaS like Heroku which is 100% at risk to EC2, you can't do it.
I've seen more failures which take out multiple AZs than which take out only a single AZ. So, a prudent person would split their application across regions (which are relatively shared nothing, except for admin/account level stuff), but Amazon goes out of its way to not make that easy -- you're using the public Internet, pay higher costs, etc.
The right choice is probably EC2 plus a non-EC2 provider (your own hosted stuff, another cloud (?), etc.), with protection in case either goes down. But that is a relatively lot of work, and if you're on a PaaS like Heroku which is 100% at risk to EC2, you can't do it.
Kind of sucks.