Turns out that "availability zones" in cloud parlance seem to have nothing to do with geographical availability. Apparently they're logical splits and are more about billing than anything.
> An Availability Zone is one or more discrete data centers with separate and redundant power infrastructure, networking, and connectivity in an AWS Region. Availability Zones in a Region are meaningfully distant from each other, up to 60 miles (~100 km) to prevent correlated failures, but close enough to use synchronous replication with single-digit millisecond latency.
Elsewhere in this threat comments mention AZ turning out in practice to be different areas of the same building, or just a matter of opinion and some config.
10s of miles is close enough that they are functionally in the same place in a military context though. The latest cheap massive wave attack drones fly hundreds of miles and hour which puts the DCs less than a minute apart by flight time. This means if you want protection against those risks you have to use multiple regions instead of, or in addition to multiple AZs.
