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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 http://www.jackofallclouds.com/2009/09/anatomy-of-an-amazon-ec2-resource-id/ 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, 2010 at 3:24

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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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Back in 2012, "Mary@AWS" in this AWS forum entry mentioned that:

Instance IDs are unique, you will not have the same instance ID in multiple regions.

so that's from the horse's mouth, at least across multiple regions of the one account. This was even before the longer ids were introduced.

No mention of global uniqueness across accounts though.

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