An Amazon Machine Image (AMI) is a template that contains a software configuration (for example, an operating system, an application server, and applications.
The Amazon machine Images provides the necessary information required to launch an instance.
You must select an AMI when you launch an instance.
If you want to launch multiple instances using same configurations, You can do it from single AMI.
Also you can use different AMI’s to launch different EC2 Instances with Different configurations.
AMI includes:
one or more EBS snapshots, Which means , by default each ec2 instance is attached with root volume , It will create a backup of the volume as well.
A block device mapping that specifies that volume to be attached to the instance when it’s launched.
Prerequisite:
One running EC2 Instance.
Creating your Own AMI:
You can launch an instance from existing AMI, make configuration changes, customize the instance, then save this upudated configuration as Custom AMI.