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Are Amazon EC2 IDs (instance, volume, snapshot, etc) across regions? For example, is it possible, albeit unlikely, for instance ID i-1a2b3c4d to appear in both eu-west-1 and us-east-1?

I have seen Is the Amazon EC2 instance id unique forever? and followed the link to which states:

Note that since each EC2 region is a completely separate system, the IDs in each region are independent of each

This leads me to believe that it is at least possible.

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I would assume it is possible. – Rob Olmos Nov 9 '10 at 3:24
up vote 0 down vote accepted

I took a look around the Developer Guide and API Reference and nowhere in either of them could I find any guarantee that the instance id would be unique among all availability zones.

The only link I could really find online (besides the one you posted) was this serverfault question which includes a post by a guy named 'jedberg' who says he contacted Amazon support and asked whether you would ever get a duplicate instance id. Their response was:

"Instance ids are unique. You'll never receive a duplicate id. However, the current format of the instance id is an implementation detail that is subject to change. If you use the instance id as a string, you should be fine."

Which doesn't specifically say that they're unique per availability zone, and does say that they make a guarantee to provide a unique instance id.

Given no concrete indication either way, I'd err on the side of caution and assume you could receive a duplicate in another availability zone. If you're really not sure, you may want to put a request in with Amazon support to ask for clarification (and post their response here!).

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There's no guarantee of global uniqueness, but today they are globally unique.

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