One problem which we've seen before is: If a large percentage of AWS infrastructure goes down, the customers don't just quietly suffer. Instead they scramble to try and launch infrastructure in other zones or regions, which creates a cascading series of load spikes throughout the AWS system.

AWS is a fascinating science experiment. Pity about the websites, though.

It's now yellow with this: "9:27 PM PDT We continue to investigate this issue. We can confirm that there is both impact to volumes and instances in a single AZ in US-EAST-1 Region. We are also experiencing increased error rates and latencies on the EC2 APIs in the US-EAST-1 Region."

AWS has been historically bad at reporting the severity of their outages promptly.