An EBS snapshot is a backup of a single EBS volume. The EBS snapshot contains all the data stored on the EBS volume at the time the EBS snapshot was created.
An AMI image is a backup of an entire EC2 instance. Associated with an AMI image are EBS snapshots. Those EBS snapshots are the backups of the individual EBS volumes attached to the EC2 instance at the time the AMI image was created.
As a Backup Strategy, Should You Create AMI Images or EBS Snapshots?
The answer to this depends on many factors, including your restore time objective, desired restore procedure, and many other business-related factors.
If your restore objective is to create a fresh EC2 instance quickly to replace a failed EC2 instance, then creating AMI images is definitely the way to go.
If your EC2 instance contains a mix of static EBS volumes (for example, a non-changing root volume) and dynamic EBS volumes (for example, a data volume), then creating EBS snapshots may be better.
Since EBS snapshots can be thought of as incremental, you only pay for the storage of the changed data. So creating multiple EBS snapshots of a non-changing EBS volume will not incur high charges.
The process of creating an AMI image will also create EBS snapshots. So even if you need to restore a single EBS volume, you can do so from the individual EBS snapshot.
For these reasons, unless there are business factors weighing against it, we recommend creating AMI images instead of just EBS snapshots.