An Amazon Machine Image (AMI) provides the information required to launch an instance. You must specify an AMI when you launch an instance. You can launch multiple instances from a single AMI when you need multiple instances with the same configuration. You can use different AMIs to launch instances when you need instances with different configurations.
An AMI includes the following:
One or more EBS snapshots, or, for instance-store-backed AMIs, a template for the root volume of the instance (for example, an operating system, an application server, and applications).
Launch permissions that control which AWS accounts can use the AMI to launch instances.
A block device mapping that specifies the volumes to attach to the instance when it’s launched.
Repeatability - Instead of manually launching and configuring each server, use an AMI to ensure that all the servers that are supposed to be identical actually are identical.
Resuability - Use the AMIs you used for your production instances for your test instances too, to ensure that your test environment is the same as your production environment.
Recoverability - If an instance fails, launch an identical one automatically to replace it, using the same configuration as the server it’s replacing.
Marketplace activities - Use pre-made AMIs from the AWS Marketplace to launch custom software packages.
Backup - Create AMIs of your currently deployed instances to maintain point-in-time backups from which you can restore your instances.