Customize EBS volume attachment on aws_instance, from an AMI with multiple volumes

Hi,

I am deploying an aws_instance from a pre-existing custom AMI. That AMI has 3 different volumes, the root device, plus two additional EBS volumes.

I am able to map the three EBS volumes within the aws_instance using root_block_device plus a dynamic block on ebs_block_device:

aws_instance "myinstance" {
  root_block_device {
    (...attributes...)
  }

  dynamic "ebs_block_device" {
    for_each = [
      for block_device in data.aws_ami.myami.block_device_mappings : {
        device_name = block_device.device_name
        volume_type = var.volume_type
        volume_size = var.volume_size
        (...other attributes...)
      }
      if block_device.device_name != data.aws_ami.myami.root_device_name
    ]
    content {
      device_name           = ebs_block_device.value.device_name
      volume_type           = ebs_block_device.value.volume_type
      volume_size           = ebs_block_device.value.volume_size
      (...other attributes...)
    }
  }
}

However, this approach runs into Terraform’s limitation of not detecting any changes (see “NOTE”) if I wanted to change volume_size or volume_type for the EBS volumes.

What I would like is to map those two additional EBS volumes from the AMI using aws_ebs_volume and aws_volume_attachment, so that I could in the future easily change, add, or remove them using only Terraform (not a mix of changing them manually and then adjusting the Terraform configuration).

I am able to come up with the resource definition to pull the correct details for aws_ebs_volume and aws_volume_attachment (namely pointing to the correct snapshot_id from the AMI), but if I specify the ami attribute on aws_instance, that immediately attaches all three volumes when the instance is deployed, making Terraform fail when it tries to do my volume attachment.

Is this possible somehow? How can I tell Terraform to attach only the root device, but let me take care of attaching the additional volumes from the AMI?

Thank you,
Tiago