Amazon EC2 allows you to set up and configure everything about your instances from your operating system up to your applications. An Amazon Machine Image (AMI) is simply a packaged-up copy of your root file system. An AMI contains all the necessary bits to set up and boot an Amazon EC2 instance. Your AMIs are your unit of deployment. You might have just one AMI or you might compose your system out of several building block AMIs (e.g., webservers, appservers, and databases).
This section details how to build your own AMIs and how to store them in Amazon S3. In addition, it covers booting existing images, and bundling those (after making any required changes). Re-bundling modified versions of existing AMIs provides an easy way to build up a range of different machine images from a pool of existing base images. Amazon EC2 provides base AMIs to get you started.