What is the a,b,c,d,e after the Amazon Availability Zone? (example: us-east-1d)

Question

Amazon uses zones that look like this: us-east-1d. I can find plenty of documentation about us-east-1, etc... but I do not see any reference to the a,b,c,d,e. What does this letter represent?

Solution

The letters actually show the Availability Zone: in us-east-1d notation, us-east-1 is the Region's ID, and d is AZ's identifier.

For example, US West has (at this very moment) two Regions assigned: us-west-1 (Northern California) and us-west-2 (Oregon). I'd suggest checking Regions and Availability Zones docpage for further details.

Note that availability zones are assigned per account:

To ensure that resources are distributed across the Availability Zones for a region, we independently map Availability Zones to identifiers for each account. For example, your Availability Zone us-east-1a might not be the same location as us-east-1a for another account.

... so 'a', 'b', etc. are logical, not physical identifiers of Availability Zones.

Comments

[jcalfee314]

There is only one section that hints to what this is. They compare only 1a to 1a across accounts. I think the docs really skip this topic. This is the text I'm referring to: """To ensure that resources are distributed across the Availability Zones for a region, we independently map Availability Zones to identifiers for each account. For example, your Availability Zone us-east-1a might not be the same location as us-east-1a for another account."""

[raina77ow]

Yes, you're right: the very important point about AZ identifiers is that they're assigned per account (and do not identify a fixed entity). That makes sense, as actual Region (most definitely) has far more then 4-5 AZs in disposal, but needs to balance their load.

[Yehuda Clinton]

Are they cross compatible?