Building Machine Images With Packer

HarshiCorp's Packer automates building machine images. Using Packer, you can use a single set of provisioners to build images for multiple builders (such as VirtualBox, Digital Ocean, and Google Cloud).

Building Vagrant Boxes

Vagrant boxes are machine images that have been packaged for use with Vagrant. By convention, this means they have a vagrant user, are configured for passwordless sudo, and may even have the VirtualBox Guest Additions installed. The Vagrant cloud is a repository of such boxes.

While many boxes include additional software (for instance, a fully configured LAMP stack), base boxes include a bare operating system and are meant to be configured and repackaged for your specific needs (for instance, a custom stack for your web application).

Using Packer To Build Vagrant Boxes

For many use cases, it is enough to repackage an existing Vagrant box.

But let's say you're planning a project that requires a local development environment, a staging environment, and a production environment. You have a distributed team using different operating systems so your development environment must be reproducible and virtualized. Due to external constraints, the staging environment must be hosted on Cloud Provider A and the production environment must be deployed to Cloud Provider B. You're expecting a lot of traffic and need a load balancer in front of several servers. You've done this before and have a very specific stack in mind.

Enter Packer.

Packer allows you to build machine images for multiple platforms using a single point of provisioning. You define a set of builders, which are the platforms you want to export images to, and a set of provisioners, which can range from shell to Ansible, Chef, and Puppet. Packer creates machines on each platform, provisions on each such machine, shuts down the machines, exports platform-specific images, and destroys the machines. What's left is a set of platform-specific images that can be used to create multiple instances on each platform.

Here is a typical packer project structure:

.
├── README.md
├── ansible
│   ├── main.yml
│   └── requirements.yml
├── http
│   └── preseed.cfg
├── iso
│   └── ubuntu-18.04.1-server-amd64.iso
├── scripts
│   ├── ansible.sh
│   ├── cleanup.sh
│   ├── init.sh
│   └── init_vagrant.sh
├── secrets
│   ├── do.json
│   └── gcloud.json
├── ubuntu18041.json
└── vagrant
    └── Vagrantfile

Almost everything in the above layout is optional except the main Packer configuration file, (named ubuntu18041.json in the example above). This file defines the set of builders and provisioners. Unless instructed otherwise, Packer will run all provisioners will against all builders.

secrets/gcloud.json must be generated from your Google Cloud account. secrets/do.json should be a JSON object with a single property, do_token, whose value should be set to your Digital Ocean API token: { "do_token": "<< YOUR TOKEN >>" }.

To validate your Packer configuration, run

packer validate -var-file=secrets/do.json ubuntu18041.json

To build your images, run

packer build -var-file=secrets/do.json ubuntu18041.json

To build images only for a specific builder -- for instance, VirtualBox -- run

packer build -only virtualbox-iso -var-file=secrets/do.json ubuntu18041.json

Once built, to add an image to Vagrant, run

vagrant box add packer-ubuntu-18041-amd64 vagrant/packer-ubuntu-18041-amd64.box

And then to use it in a Vagrantfile you can simply do

# -*- mode: ruby -*-
# vi: set ft=ruby :

Vagrant.configure("2") do |config|
  config.vm.box = "packer-ubuntu-18041-amd64"
end