Alon Swartz - Wed, 2010/03/24 - 12:35 -
Each Amazon EC2 instance has associated metadata, as well as user data supplied when launching the instance. The meta and user data is instance-specific, and therefore only accessible to the instance.
The data is useful on several levels, such as configuring SSH public keys, programmatically configuring the instance according to certain criteria, or even executing user supplied initialization scripts.