Building consistent virtual machines with Packer and Vagrant

I’ve been using Vagrant to manage local development environments for a while, but there are subtle differences between the base Ubuntu Vagrant box and the Ubuntu Cloud Images I typically use in production. Since the base set of packages don’t match exactly, builds would occasionally fail on AWS after working fine locally. While I always caught these issues before they went live, the mismatch was annoying at best.

While looking to simplify a server image creation scheme, I saw an opportunity to standardize the base VMs across environments. My main goal was to replace a bespoke Amazon Machine Image (AMI) creation script with Packer, which not too coincidentally ties in quite well with Vagrant.

The idea was to use a nearly identical base machine as a starting point both locally and on AWS. The first step is to get an Ubuntu Cloud Image suitable for use in Packer’s Virtualbox builder. When passed the name of the Ubuntu release you wish to use (e.g. $ dlbox.sh trusty), the following script will unzip the .ovf/.vmdk files into an folder named ubuntu.$RELEASE.box.

#!/usr/bin/env bash
set -eu

BOX_URL=https://cloud-images.ubuntu.com/vagrant/$1/current/$1-server-cloudimg-amd64-vagrant-disk1.box
mkdir -p ubuntu.$1.box
curl $BOX_URL | tar -x -C ubuntu.$1.box

Next you need to identify a matching EC2 image with the AMI Locator. At this moment, the EBS equivalent is ami-e63b3e8e.

With that, we can fill out a rudimentary packer.conf. This will launch matching machines locally and on AWS. Provisioning steps are very situation dependent, so I left them out.

{
  "variables": {
    "release_id": null,

    "source_ovf": "ubuntu.trusty.box/box.ovf",
    "source_ami": "ami-64e27e0c",

    "vagrant_private_key": "{{ env `HOME` }}/.vagrant.d/insecure_private_key"
  },
  "builders": [
    {
      "name": "vagrant",
      "type": "virtualbox-ovf",
      "source_path": "{{ user `source_ovf` }}",
      "guest_additions_mode": "disable",
      "ssh_username": "vagrant",
      "ssh_key_path": "{{ user `vagrant_private_key` }}",
      "ssh_wait_timeout": "30s",
      "shutdown_command": "echo 'packer' | sudo -S shutdown -P now"
    },
    {
      "name": "aws",
      "source_ami": "{{ user `source_ami` }}",
      "ami_name": "aws.{{user `release_id`}}.{{isotime \"2006-01-02.0304\"}}",
      "type": "amazon-ebs",
      "region": "us-east-1",
      "instance_type": "t1.micro",
      "ssh_username": "ubuntu"
    }
  ],
  "post-processors": [
    [
      {
        "type": "vagrant",
        "only": ["vagrant"],
        "output": "web.{{user `release_id`}}.box"
      }
    ]
  ]
}

You can use the above config with this command (omit the -only flag to enable the AWS builder).

$ packer build -var 'release_id=foo' -only=vagrant packer.json

Obviously there are many customizations you can make to suit your situation. I actually feed a previously built image into packer as the source Box/AMI (just change/override the source_* variables). This enables a configuration management system such as Salt, Ansible or Chef to update the images incrementally, potentially saving a ton of time.

This isn’t an exhaustive tutorial on Packer, which has excellent documentation and a helpful community.