If you use Ubuntu Linux on AWS EC2, this will find the correct image to use. It returns latest official AMI ID for your Ubuntu release, CPU architecture, and AWS region.
The result is placed on the clipboard so you can paste it into AWS.
Ubuntu frequently updates images to incorporate the latest security updates. Older versions of Ubuntu are also updated, so the AMI that you use should be looked up fresh each time.
http://www.packal.org/workflow/get-latest-ubuntu-ami