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There's a big note on the terraform page documenting the feature on which it's based.

Currently, changes to the ebs_block_device configuration of existing resources cannot be automatically detected by Terraform. To manage changes and attachments of an EBS block to an instance, use the aws_ebs_volume and aws_volume_attachment resources instead. If you use ebs_block_device on an aws_instance, Terraform will assume management over the full set of non-root EBS block devices for the instance, treating additional block devices as drift. For this reason, ebs_block_device cannot be mixed with external aws_ebs_volume and aws_volume_attachment resources for a given instance.

I suppose I can do it that way. It is odd behavior since nothing is changing. I even read where others have managed to get this working before (https://github.com/pulumi/pulumi-aws/issues/999). Since I am only adding a single non-root EBS device and getting this issue, I think is why I am confused.

The

ignoreChanges

option will get you over the problem so long as you don't plan on, y'know, making any changes...

Gotcha. Thank you.