Amazon EC2 Service Level Agreement
aws.amazon.com
aws.amazon.com
For the record, I’m running in us-west-2 and have barely had any issues in the past 3+ years but I do wish they were more transparent with their status.
Most of the redundancy that powers EC2s availability SLA is at the infrastructural level; power, network and so on. These resources are shared by all of EC2. But physical redundancy is really the "easy" part of an availability SLA, if it were just a matter of buying more routers and UPS's, it would be straightforward to hit any number of nines. Instead, the real work is all of the practices and culture that's been built up around managing a system at scale. The change process, the deployment process, and the root-cause-analysis process each are part of this; team members wouldn't lower their standards or depart from the process based on price, it'd be a very un-natural way to do things!
No such option exists anymore.
Sure, they have a Reduced Redundancy "feature". But you would be stupid to use it because RR costs more than the regular redundancy, not less. (One big hint is that it's not even listed on their regular pricing page anymore.)
That is how Amazon phases out features: Instead of raising the price, they just don't lower it. Over time, it becomes more expensive because all the other prices are going down.
With s3 it's easy: store fewer copies.
With ec2, it's much harder.
Actual availability numbers is often secondary to Big Corp customers. The benefit of the CYA/SLA agreement, is that when shit does hit the fan, as the manager you get to shrug and say "well, we bought the improved SLA, not my fault Amazon failed to deliver".
If you want to be sure you get paid if you’re offline, your workloads have to be spread across all AZs in the region.
Otherwise your subset of AZs can go down and because it’s not the whole region you won’t get paid.