packer.json

{
  "variables": {
    "access_key": "{{env `aws_id`}}",
    "secret_key": "{{env `aws_key`}}",
    "source_ami": "{{env `ami_id`}}",
    "ami_name": "{{env `ami_name`}}",
    "region": "{{env `region`}}",
    "drone_build_number": "{{env `DRONE_BUILD_NUMBER`}}",
    "drone_repo_name": "{{env `DRONE_REPO_NAME`}}"

  },
  "sensitive-variables": ["access_key", "secret_key"],
  "builders": [
    {
      "type": "amazon-ebs",
      "access_key": "{{user `access_key`}}",
      "secret_key": "{{user `secret_key`}}",
      "region": "{{user `region`}}",
      "source_ami": "{{user `source_ami`}}",
      "instance_type": "t2.medium",
      "encrypt_boot": true,
      "communicator": "none",
      "run_tags":{
            "Name": "Packer Build [{{user `drone_repo_name`}}: {{user `drone_build_number`}}]"
      },
      "ami_name": "{{user `ami_name`}} copied from {{user `source_ami`}}"
    }
  ]
}