http://ec2-downloads.s3.amazonaws.com/AmazonLinuxAMIUserGuide.pdf

For use only in EC2.  Closest to CentOS.

32 and 64 bit versions.

The kernel IDs listed in Management Consoles for instances do not  correspond
in any obvious way to uname strings or rpm name/versions.

PRE-INSTALLED
    C2 CLI  (must set up env.)
    CloudInit  (typically or originally from Ubuntu)

Package-compatible with CentOS.

yum comes pre-configured for the Amazon Linux repository.