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

When selecting an AMI, select from a trusted source.

The AMI number is just a unique identifier for a particular image that someone published. The title (e.g. Ubuntu 12.04LTS) is just a claim by the person who published the AMI about what is on it.

If you get your AMI from a source that is not known to be trustworthy, it could potentially contain built-in security holes, pre-installed spam relays, etc.

From Amazon

You launch AMIs at your own risk. Amazon cannot vouch for the integrity or security of AMIs shared by other EC2 users. Therefore, you should treat shared AMIs as you would any foreign code that you might consider deploying in your own data center and perform the appropriate due diligence.

Ideally, you should get the AMI ID from a trusted source (a web site, another EC2 user, etc). If you do not know the source of an AMI, we recommend that you search the forums for comments on the AMI before launching it. Conversely, if you have questions or observations about a shared AMI, feel free to use the AWS forums to ask or comment.

Amazon's public images have an aliased owner and display amazon in the userId field. This allows you to find Amazon's public images easily.

http://docs.amazonwebservices.com/AWSEC2/latest/UserGuide/AESDG-chapter-usingsharedamis.html#usingsharedamis-security

Personally I select AMIs published well-known entities like Amazon or RighScale.

Answer 2

AMI is just an image of a disk. It has nothing to do with type(micro). You can create multiple AMIs from the same instance and they will have have different IDs.

Answer 3

They are just different images. You could make two images from the same machine a minute after each other with no changes on the machine at all and they will have different AMI id's. The AMI ID is just applied at the time the image is created as a unique identifier, it infers nothing about the uniqueness of the image content.

Answer 4

An infinite number of people can create an infinite number of disk image variations that are still "64-bit micro Ubuntu 12.04 LTS". Just like there are over 500 million PCs in the world running Windows 7 64-bit, yet their hard drives all contain different data. If you wanted to be able to differentiate Joe's disk image from Sue's disk image, you'd need to give them different identifiers. That's why the AMI numbers are different.