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Comment by TeMPOraL | Hacker News Reader

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.

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> 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.

> https://docs.aws.amazon.com/whitepapers/latest/aws-fault-iso...

They are far enough apart that tornados, floods, and fires cannot simultaneously impact multiple.

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.

Yeah that’s true of Azure and of GCP but not AWS. Azure clearly states this in their documentation. Nobody was trying to hide it from you.

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.

A targeted, coordinated attack can compromise multiple AZs.

But AFAIK AWS has only reported data loss in mec1-az2.

Cross-AZ services like S3 should have no data loss, unless there is more damage than AWS has currently published.

How often does an AZ go down while the other 2 still work?

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