How to create a EC2 instance from snapshot in cloudformation?

Question

I'd like to specify the snapshot id which would be used to create a root device image for a EC2 instance created with cloudformation. How do I do that?

I could only find a way to make volume from a snapshot, but no way to use it in the instance.

Answer 1

If you want to use an EBS snapshot as the basis of the root disk (EBS volume) for an instance, you need to first register the snapshot as an AMI (e.g., using ec2-register).

Make sure to specify the correct architecture and kernel (AKI) when you register the snapshot as an AMI.

Alternatively, instead of taking a snapshot and registering it as separate steps, you could use the ec2-create-image command/API/console function to perform the snapshot and registration in a single step. This also takes care of picking the right architecture, kernel, and other parameters.

Once you have an AMI, you can tell CloudFormation to use that AMI when running a new instance.

Answer 2

I concur. This has nothing to do with cloudformation, but I just did this following a crippling 'do-release-upgrade'. It's just a matter of creating an image from the snapshot, and in my case making sure to change the virtualization type to "hardware assisted virtualization" (HVM). Then you can just launch the resulting image (AMI).