What most people don't realize is that the magic isn't in handling the system itself; the magic is making authorization appear to be zero-cost.

In distributed systems authorization is incredibly difficult. At the scale of AWS it might as well be magic. AWS has a rich permissions model with changes to authorization bubbling through the infrastructure at sub-millisecond speed - while handling probably trillions of requests.

This and logging/accounting for billing are the two magic pieces of AWS that I'd love to see an article about.

Note that S3 does AA differently than other services, because the permissions are on the resource. I suspect that's for speed?