AMIs created in one region cannot be used to create instances in another region. However you can get round this by copying the AMI to another region first.
You can also modify access permissions of the AMI, in the following ways:
- Make the AMI public, so anyone can use it by finding it on the marketplace
- Specify a list of AWS account names that can access the ami
However the region restriction still applies in both of the above cases.
An AMI is made up of 3 parts:
- a snapshot of the root volume, /dev/sda1
- launch permissions, i.e. is it a public ami, or restricted to a particular aws account
- block device mappings. This means that an ami can be made up of several ebs snapshots in addition to /dev/sda1
You can create an AMI from an existing EBS snapshot, as long as the snapshot is taken of the root volume, /dev/sda1.
AWS stores Both AMI and snapshots in S3.