In Amazon Web Services what does AMI number signify

Question

I am trying to create an Amazon EC2 instance. I want to create a micro, 64-bit, Ubuntu 12.04 LTS instance.

In Amazon Web Services I have seen all instance have AMI numbers. Now I found two ami(s) with numbers ami-8a7f3ed8 and ami-b8a8e9ea. both looks same to me - micro, ebs-based, 64-bit Ubuntu 12.04LTS images.

If so, what is the difference and why two number for the same machine image?

Answer 1

AMIs are machine images. They are essentially snapshots that you can use to create a new instance. It is possible to have 2 snapshots that have exactly the same data.

For instance, you can create an AMI from an existing instance to get a new AMI with a new number. Each time you repeat the process for the machine, you will create another AMI with a different number. If nothing has changed on the source machine, all of these AMIs will be virtually identical.

Answer 2

I believe the AMI IDs don't signify anything in particular, but are specific to regions, so an otherwise identical US-WEST AMI will have a different ID from a US-EAST one, and so on.

If you're using Ubuntu, you may want to look at the official Ubuntu AMIs:

https://help.ubuntu.com/community/EC2StartersGuide#Official_Ubuntu_Cloud_Guest_Amazon_Machine_Images_.28AMIs.29

Answer 3

AMI ID is a combination of OS, architecture, ebs, zone and it's release. You should check if the zones/regions are also identicaly for the AMI's you listed.