Virtual machines with Vagrant

What is Vagrant?

Vagrant is basically a wrapper around virtual machine providers like VirtualBox, VMware or AWS. You simply need to create a config file (called Vagrantfile) in a folder, use vagrant up and you've got a VM up and running in less than 30 seconds! The only required entry in the config file is the base image to use, but you can configure multiple properties like port forwarding, IP address, shared folders, amount of memory, script to run on first startup of the machine, etc. This is very useful for sharing, as you only need to share a config file instead of a huge VM folder. And it can be version controlled!

Required software

For this post, I will use VirtualBox, as it's free, well supported and is the only available provider out of the box (you need to install plugins for the others). Make sure you have VirtualBox and Vagrant installed before continuing. Vagrant also uses ruby, but you don't need to install it since it's embedded in Vagrant.

Getting started

Here is the most basic Vagrantfile you can do.

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

VAGRANTFILE_API_VERSION = "2"

Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
  config.vm.box = "ubuntu/trusty64"
end

As you can see, this is plain ruby, so you could use variables, loops, conditions, etc. Don't panic if you don't know ruby, the Vagrantfile can be read like a regular config file.

The base image (called "box") I used is Ubuntu 14.04 64 bits.

Put this file in a new folder and use vagrant up to create the virtual machine. Remember when I told you it'd take 30 seconds?

The box first needs to be downloaded to a local repository, but future machines using this box will use the local version.

You should see the VM in the VirtualBox GUI, but do not edit the configuration there since Vagrant will probably override your settings. Edit the Vagrantfile instead.

When the VM is ready, use vagrant ssh to SSH into it. Most boxes in Vagrant run in headless mode, but if you need a desktop environment, boxcutter's Ubuntu desktop box seems to work well.

To shutdown the VM, use vagrant halt. To destroy it, use vagrant destroy. To reboot it, use vagrant reload.

Configuration

You can also use vagrant init to create a Vagrantfile with a bunch of options commented out. Let's review the most interesting ones.

Box

# Every Vagrant development environment requires a box. You can search for
# boxes at https://atlas.hashicorp.com/search.
config.vm.box = "base"

In the previous section, I used the official Ubuntu 14.04 box, but you can find more at https://atlas.hashicorp.com/search. The value should be the name of the box (ubuntu/trusty64 for example).

You can also use config.vm.box_url if the box is not in Hashicorp's Atlas. In this case you need a full URL.

Port forwarding

# Create a forwarded port mapping which allows access to a specific port
# within the machine from a port on the host machine. In the example below,
# accessing "localhost:8080" will access port 80 on the guest machine.
config.vm.network "forwarded_port", guest: 80, host: 8080

Port forwarding can be useful if you need to access a service in the VM from a machine on the network but don't want to expose the whole VM.

Private network

# Create a private network, which allows host-only access to the machine
# using a specific IP.
config.vm.network "private_network", ip: "192.168.33.10"

This will create a "host-only network", which allows other VMs and the host to communicate together. If the interface doesn't exist on the host, it will create it.

Public network

# Create a public network, which generally matched to bridged network.
# Bridged networks make the machine appear as another physical device on
# your network.
config.vm.network "public_network"

The word public here is confusing. This will add an interface on the same network as the host. Let's say your host has IP 192.168.0.100, your VM could get 192.168.0.167, for example. This means you will be able to ping the VM from another computer in the same network. Since Vagrant is insecure by default, this is probably a bad idea.

Shared folders

# Share an additional folder to the guest VM. The first argument is
# the path on the host to the actual folder. The second argument is
# the path on the guest to mount the folder. And the optional third
# argument is a set of non-required options.
config.vm.synced_folder "../data", "/vagrant_data"

Share a folder with the host. By default, Vagrant shares the folder containing the Vagrantfile to the /vagrant folder in the VM.

Provider-specific configuration

# Provider-specific configuration so you can fine-tune various
# backing providers for Vagrant. These expose provider-specific options.
# Example for VirtualBox:
#
config.vm.provider "virtualbox" do |vb|
  # Display the VirtualBox GUI when booting the machine
  vb.gui = true

  # Customize the amount of memory on the VM:
  vb.memory = "1024"
end
#
# View the documentation for the provider you are using for more
# information on available options.

Note that customizing the amount of memory is done on a per-provider basis.

Provisionning

# Enable provisioning with a shell script. Additional provisioners such as
# Puppet, Chef, Ansible, Salt, and Docker are also available. Please see the
# documentation for more information about their specific syntax and use.
config.vm.provision "shell", inline: <<-SHELL
  sudo apt-get update
  sudo apt-get install -y apache2
SHELL

Provisionning is used to setup the VM once it is booted. Of course, you can simply SSH into the machine and install what you want in it, but adding it in the Vagrantfile will automate the process if you need multiple VMs or want to share it.

You can add your script inline (like the example), but you can also use a script file or configuration managements systems like Chef, Puppet, Ansible or Salt. If you use scripts, make sure they are non-interactive! (Add the -y flag to apt-get install for example).

Provisionning happens in these situations:

• On the first vagrant up
• On a running VM, vagrant provision
• vagrant up --provision
• vagrant reload --provision

Defining multiple machines in a Vagrantfile

To do so, use config.vm.define in the Vagrantfile.

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

VAGRANTFILE_API_VERSION = "2"

Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
  config.vm.box = "ubuntu/trusty64"

  config.vm.define "alice" do |alice|
    alice.vm.hostname = "alice"
    alice.vm.network :private_network, ip: "192.168.33.210"
    alice.vm.provision "shell", inline: "echo 192.168.33.211 bob >> /etc/hosts"
  end

  config.vm.define "bob" do |bob|
    bob.vm.hostname = "bob"
    bob.vm.network :private_network, ip: "192.168.33.211"
    bob.vm.provision "shell", inline: "echo 192.168.33.210 alice >> /etc/hosts"
  end
end

Here, we defined 2 VMs, alice and bob, that both have a sub-config setting their hostname and a private network IP and adding the other machine in the hosts file. They also inherit from the top level config, so they will both use the box ubuntu/trusty64. To define it per-machine, just make sure you use the per-machine variables (alice and bob) in their do...end block.

The Vagrant command line differs when there is multiple machines defined. Commands that only make sense for a single machine, such as vagrant ssh, require you to include the name of the machine as an argument: vagrant ssh bob. Other commands, such as vagrant up, will operate on every machine by default, but you can also specify the target: vagrant up alice.

More info

This post covered common usage of Vagrant, but you can do more with it, such as pushing code to Heroku or sharing your VM over SSH. The official documentation is very well structured, so make sure you have a look!