Awesome

NixOS Vagrant Plugin

This plugin adds nix provisioning for NixOS guests to Vagrant.

Vagrant 1.6.4+ itself already provides capabilities to change the hostname and networking settings by generating /etc/nixos/vagrant-{network,hostname}.nix files but then doesn't invoke nixos-rebuild switch.

This plugin takes care of that, plus gives different ways for the user to configure the VM using a special DSL.

Install:

NOTE: this project is a fork of the vagrant-nixos gem. Both can't be installed at the same time.

$ vagrant plugin install vagrant-nixos-plugin

Example Vagrantfile

Vagrant.configure("2") do |config|

  # Use a suitable NixOS base. VM built with nixbox are tested to work with
  # this plugin.
  config.vm.box = "zimbatm/nixos-15.09-x86_64"

  # set hostname
  config.vm.hostname = "nixy"

  # Setup networking
  config.vm.network "private_network", ip: "172.16.16.16"

  # Add the htop package
  config.vm.provision :nixos,
    run: 'always',
    expression: {
      environment: {
        systemPackages: [ :htop ]
      }
    }

end

In the above Vagrantfile example we provision the box using the :expression method, which will perform a simple ruby -> nix conversion. :expression provisioning creates a nix module that executes with pkgs in scope. It is roughly equivilent to the below version that uses the :inline method.

config.vm.provision :nixos,
  run: 'always',
  inline: %{
{config, pkgs, ...}: with pkgs; {
  environment.systemPackages = [ htop ];
}
  },
  NIX_PATH: '/vagrant/nixpkgs'

The above example also shows the optional setting of a custom NIX_PATH path.

You can also use an external nix configuration file:

config.vm.provision :nixos, run: 'always', path: "configuration.nix"

If you need provisioning to be included explicitly during rebuild use:

config.vm.provision :nixos,
  run: 'always',
  path: “configuration.nix”,
  include: true

You can enable verbose provision output during rebuild process with:

config.vm.provision :nixos,
  run: 'always',
  path: “configuration.nix”,
  verbose: true

If you need to use functions or access values using dot syntax you can use the Nix module:

config.vm.provision :nixos, expression: {
  services: {
    postgresql: {
      enable: true,
      package: Nix.pkgs.postgresql93,
      enableTCPIP: true,
      authentication: Nix.lib.mkForce(%{
        local all all              trust
        host  all all 127.0.0.1/32 trust
      }),
      initialScript: "/etc/nixos/postgres.sql"
    }
  }
}

How it works

In nixos we don't mess around with the files in /etc instead we write expressions for the system configuration starting in /etc/nixos/configuration.nix.

This plugin sets some ground rules for nixos boxes to keep this configuration clean and provisioning possible.

Box creators should ensure that their configuration.nix file imports an nix module /etc/nixos/vagrant.nix which will be overwritten by vagrant-nixos-plugin during vagrant up or vagrant provision and by vagrant for the /etc/nixos/vagrant-hostname.nix and /etc/nixos/vagrant-network.nix files.

When declaring the provisioner it is recommended to add the run: 'always' attribute to make sure that changes to the Vagrantfile are reflected during reload.

See the configuration in our NixOS packer template for an example.

Issues

It's a bit slow on the initial boot/provision at the moment as it must run nixos-rebuild several times. This is far from ideal I'm sure I'll find a better place to hook in the rebuild step soon.