I have been trying to find out how to select uefi boot mode for aws_ami as it is required for the instance to start up properly. This functionality appears to have been available since March 2021 however I did not find any documentation or even code reference similar to “EnaSupport”.
Is there a way to change the boot mode to uefi?
This is a setting or flag on the AMI level. So you cannot change it when booting however when the image is built or searched for.
Do you select an UEFI Image to boot with?
Yes, after uploading a VMDK to S3 then snapshot created to aws_ami{} which I need to assign uefi to the boot mode. It is similar to what is described in the Amazon EC2 register image page if doing from command line. I just have not found anything doc reference for the same action in terraform aws provider.
Ah, now I see.
Well, indeed it isn’t included in the codebase.
I’ve created a new issue within the terraform-provider-aws repo.
It’s now in the Changelog for upcoming v4.0.0. 
Thanks @tbugfinder ! I will keep an eye out for its release. Cheers 