This is the template file being used to create a hyperv-iso based vagrant image.

packer_template.json

{
  "builders": [
    {
      "type": "hyperv-iso",
      "communicator":"ssh",
      "iso_url": "{{user `mirror`}}/16.04/ubuntu-16.04.2-server-amd64.iso",
      "iso_checksum": "{{user `iso_checksum`}}",
      "iso_checksum_type": "{{user `iso_checksum_type`}}",
      "output_directory": "output-ubuntu-16.04-amd64-{{build_type}}",
      "vm_name": "tcdev-hyperv-ubuntu-16.04-amd64",
      "disk_size": "{{user `disk_size`}}",
      "http_directory": "./http/",
      "boot_wait": "5s",
      "generation": 2,
      "enable_secure_boot":false,
      "boot_command": [
        "<enter><wait>",
        "<f6><esc>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs><bs><bs><bs><bs><bs><bs><bs>",
        "<bs><bs><bs>",
        "/install/vmlinuz ",
        "initrd=/install/initrd.gz ",
        "net.ifnames=0 ",
        "auto-install/enable=true ",
        "debconf/priority=critical ",
        "preseed/url=http://{{.HTTPIP}}:{{.HTTPPort}}/preseed.cfg ",
        "<enter>"
      ],
      "ssh_timeout": "{{user `ssh_timeout`}}",
      "ssh_username": "vagrant",
      "ssh_password": "vagrant",
      "shutdown_command": "echo 'vagrant' | sudo -S -E shutdown -P now"
    }
  ],
  "provisioners": [
    {
      "type": "shell",
      "execute_command": "echo 'vagrant' | {{.Vars}} sudo -S -E bash '{{.Path}}'",
      "script": "scripts/setup.sh"
    },
    {
      "type": "ansible-local",
      "playbook_file": "ansible/setup.yml",
      "playbook_dir": "ansible"
    }
  ],
  "post-processors": [
    {
      "compression_level": "9",
      "output": "build/tcdev-{{build_type}}.box",
      "type": "vagrant"
    }
  ],
  "variables": {
    "compression_level": "6",
    "cpus": "1",
    "disk_size": "40000",
    "headless": "false",
    "iso_checksum": "737ae7041212c628de5751d15c3016058b0e833fdc32e7420209b76ca3d0a535",
    "iso_checksum_type": "sha256",
    "memory": "512",
    "mirror": "http://releases.ubuntu.com",
    "ssh_timeout": "60m"
  }
}