packer json

test.json

{
  "variables": {
    "my_key": "{{ env `HOME`}}/.ssh/id_dsa",
    "aws_key": "{{ env `HOME`}}/.ssh/id_aws-test_dsa",
  },
  "builders": [{
    "type": "amazon-ebs",
    "region": "us-east-1",
    "source_ami": "ami-6d1c2007",
    "instance_type": "t2.micro",
    "ami_name": "packer-centos-base-test {{timestamp}}",
    "communicator": "ssh",
    "ssh_bastion_host": "basty",
    "ssh_bastion_username": "me",
    "ssh_bastion_private_key_file": "{{user `my_key`}}",
    "ssh_username": "centos",
    "ssh_private_key_file": "{{user `aws_key`}}"
  }]
}