Why is an AMI tied to a region on ec2?

Question

I understand that when I launch an instance on ec2, that the instance has to be located on a particular data center, and that after launching you can't change that. I also understand that an AMI is created from an instance.

But what I dont understand, is when I launch an instance from an AMI, why can't I specify what region I want it to run on? Seems like it shouldnt matter, once the AMI is created you should be able to launch it in any region. What does the AMI contain that ties it to a region and why?

Answer 1

Kernels. The kernel IDs change across regions (don't ask me why). Meaning an AMI which specifies a kernel ID to be booted with can only be booted in the region this kernel ID exists.