Amazon Machine Image (AMI)

An Amazon Machine Image (AMI) provides the information required to launch an instance.
AMI comes with various base images Amazon Linux, Ubuntu, Fedora, Red Hat, Windows etc.
These images can be customized at runtime using EC2 user-data
AMI allows you to create your own customized image.
AMI Includes – One or more EBS snapshots for instance-store-backed AMIs, a template for the root volume of the instance (for example, an operating system, an application server, and applications).
You can launch multiple instances from a single AMI when you need multiple instances with the same configuration.

AMI uses S3 for storing

When you create your own AMI from the instance it requires space to store and they live in Amazon S3.
Hence you are charged for the space occupied in S3 for storing S3. So make sure you remove the AMIs which are not in use.
By default AMIs are private and locked for your account/region. They can be made public and shared with other AWS accounts if required.

Shared AMI behavior

You can share an AMI with another AWS account.
Sharing an AMI does not affect the ownership of the AMI.
You cannot associate your billing product shared by other while again sharing the AMIs to public
You can share an AMI with specific AWS accounts without making the AMI public. All you need is the AWS account IDs.

Benefits of using AMI

AMIs comes with pre-installed OS and other packages
When you use AMI to create instance you don’t need to use user-data for startup automation every time
Helps in deploying set of instances in one go faster than manually creating EC2 instances
Public AMIs help you reduce time in commissioning instances

Note:
You cannot use ADDS in AMIs as replicating the DC with same domain in multiple locations will be of no use.