I’m using packer to create AWS AMIs from a custom built image. When starting the build, I don’t know which distribution is inside the image. I start a machine using packer (aws-chroot), mount an additional volume and copy stuff from my image to that volume.

Now after I have copied all files to the correct directories, I’d like to issue a cat /etc/os-release | grep UBUNTU_CODENAME to find out the distribution I’m building an AMI for. And I would like to use this information as a tag attached to the AMI created.

This is how the relevant part of the packer file looks like:

source "amazon-chroot" "pc" {

  # start with totally empty volume
  from_scratch            = true

  # general stuff
  ami_description         = "Created from foo/packer in Build ${var.arg_build_number}"
  ami_name                = "${var.arg_ami_name}"
  ami_regions             = ["eu-central-1"]
  ami_virtualization_type = "hvm"
  region                  = "eu-central-1"
  tags = {
    Buildno  = "${var.arg_build_number}"
    Name     = "my-little-ami-${var.arg_build_number}"
  }

  # disk type/size
  nvme_device_path        = "/dev/nvme1n1p"
  device_path             = "/dev/sdf"
  root_device_name        = "/dev/xvda"
  root_volume_size        = 3
  root_volume_type        = "gp3"
  ami_block_device_mappings {
    delete_on_termination = true
    device_name           = "/dev/xvda"
    volume_type           = "gp3"
  }

  # enable fast networking
  ena_support             = true

  # force overwrite ami with same name
  # .. helpful for debug runs
  force_delete_snapshot   = true
  force_deregister        = true

  # prepare disk layout
  pre_mount_commands      = [
    "parted /dev/nvme1n1 mklabel msdos mkpart primary ext4 1M 100% set 1 boot on print",
    "mkfs.ext4 /dev/nvme1n1p1",
  ]

  # run actual host setup
  post_mount_commands = [
    "${path.root}/install_host.sh {{.MountPath}}",
  ]
}

build {
  sources = [ "amazon-chroot.pc" ]

  post-processor "manifest" {
    output = "manifest.json"
  }

}

My goal is to add another tag Codename in the tags section of the AMI. But I don’t know if it is possible to retrieve information gathered inside the build command and use it outside.

Does anybody have an idea if this is possible at all?