Nix Flakes on WSL

Published on 04/30/2022, 1489 words, 6 minutes to read

About five years ago, Microsoft released the Windows Subsystem for Linux (WSL). This allows you to run Linux programs on a Windows machine. When they released WSL version 2 in 2019, this added support for things like Docker and systemd. As a result, this is enough to run NixOS on Windows.

<Mara>

This will give you an environment to run Nix and Nix Flakes commands with. You can use this to follow along with this series without having to install NixOS on a VM or cloud server. This is going to retread a bunch of ground from the first article. If you have been following along through this entire series, once you get to the point where you convert the install to flakes there isn't much more new material here.

Installation

Head to the NixOS-WSL CI feed and download the installer.zip file to your Downloads folder. Extract the nixos-wsl-installer.tar.gz file from installer.zip. Do not extract nixos-wsl-installer.tar.gz, the wsl command will for you.

Then open Powershell and make a folder called WSL:

New-Item -Path .\WSL -ItemType Directory

<Mara>

It's worth noting that Powershell does have a bunch of aliases for common coreutils commands to the appropriate Powershell CMDlets. However these aliases are NOT flag-compatible and use the Powershell semantics instead of the semantics of the command it is aliasing. This will bite you when you use commands like wget out of instinct to download things. In order to avoid your muscle memory betraying you, the Powershell CMDlets are shown here in their full overly verbose glory.

Then enter the directory with Set-Location:

Set-Location -Path .\WSL

<Mara>

This directory is where the NixOS root filesystem will live. If you want to put this somewhere else, feel free to. Somewhere in %APPDATA% will work, just as long as it's on an NTFS volume somewhere.

Make a folder for the NixOS filesystem:

New-Item -Path .\NixOS -ItemType Directory

Then install the NixOS root image with the wsl command:

wsl --import NixOS .\NixOS\ ..\Downloads\nixos-wsl-installer-fixed.tar.gz --version 2

And start NixOS once to have it install itself:

wsl -d NixOS

Once that finishes, press control-D (or use the exit command) to exit out of NixOS and restart the WSL virtual machine:

exit
wsl --shutdown
wsl -d NixOS

And then you have yourself a working NixOS environment! It's very barebones, but we can use it to test the nix run command against our gohello command:

$ nix run github:Xe/gohello
Hello reader!

Local Services

We can also use this NixOS environment to run a local nginx server. Open /etc/nixos/configuration.nix:

{ lib, pkgs, config, modulesPath, ... }:

with lib;
let
  nixos-wsl = import ./nixos-wsl;
in
{
  imports = [
    "${modulesPath}/profiles/minimal.nix"

    nixos-wsl.nixosModules.wsl
  ];

  wsl = {
    enable = true;
    automountPath = "/mnt";
    defaultUser = "nixos";
    startMenuLaunchers = true;

    # Enable integration with Docker Desktop (needs to be installed)
    # docker.enable = true;
  };

  # Enable nix flakes
  nix.package = pkgs.nixFlakes;
  nix.extraOptions = ''
    experimental-features = nix-command flakes
  '';
}

Right after the wsl block, add this nginx configuration to the file:

services.nginx.enable = true;
services.nginx.virtualHosts."test.local.cetacean.club" = {
  root = "/srv/http/test.local.cetacean.club";
};

This will create an nginx configuration that points the domain test.local.cetacean.club to the contents of the folder /srv/http/test.local.cetacean.club.

<Mara>

The /srv folder is set aside for site-specific data, which is code for "do whatever you want with this folder". In many cases people make a separate /srv/http folder and put each static subdomain in its own folder under that, however I am also told that it is idiomatic to put stuff in /var/www. Pick your poison.

Then you can test the web server with the curl command:

$ curl http://test.local.cetacean.club
<html>
<head><title>404 Not Found</title></head>
<body>
<center><h1>404 Not Found</h1></center>
<hr><center>nginx</center>
</body>
</html>

This is good! Nginx is running and since we haven't created the folder with our website content yet, this 404 means that it can't find it! Let's create the folder so that nginx has permission to it and we can modify things in it:

sudo mkdir -p /srv/http/test.local.cetacean.club
sudo chown nixos:nginx /srv/http/test.local.cetacean.club

Finally we can make an amazing website. Open /srv/http/test.local.cetacean.club/index.html in nano:

nano /srv/http/test.local.cetacean.club/index.html

And paste in this HTML:

<title>amazing website xD</title>
<h1>look at my AMAZING WEBSITE</h1>
It's so cool *twerks*

<Mara>

This doesn't have to just be artisanal handcrafted HTML in bespoke folders either. You can set the root of a nginx virtual host to point to a Nix package as well. This will allow you to automatically generate your website somehow and deploy it with the rest of the system. Including being able to roll back changes.

And then you can see it show up with curl:

$ curl http://test.local.cetacean.club
<title>amazing website xD</title>
<h1>look at my AMAZING WEBSITE</h1>
It's so cool *twerks*

You can also check this out in a browser:

a browser window titled "amazing website xD" with the header "look at my AMAZING WEBSITE" and content of "It's so cool twerks"

Installing `gohello`

To install the gohello service, first we will need to convert this machine to use NixOS flakes. We can do that really quick and easy by adding this file to /etc/nixos/flake.nix:

<Mara>

Do this as root!

{
  inputs = {
    nixpkgs.url = "nixpkgs/nixos-unstable";
  };

  outputs = { self, nixpkgs, ... }: {
    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        ./configuration.nix

        # add things here
      ];
    };
  };
}

Then run nix flake check to make sure everything is okay:

sudo nix flake check /etc/nixos

And finally activate the new configuration with flakes:

sudo nixos-rebuild switch

<Mara>

Why don't you have the --flake flag here? Based on what I read in the documentation, I thought you had to have it there.

<Cadey>

nixos-rebuild will auomatically detect flakes in /etc/nixos. The only major thing it cares about is the hostname matching. If you want to customize the hostname of the WSL VM, change the nixos in nixosConfigurations.nixos above and set networking.hostName to the value you want to use. To use flakes explicitly, pass --flake /etc/nixos#hostname to your nixos-rebuild call.

After it thinks for a bit, you should notice that nothing happened. This is good, we have just converted the system over to using Nix flakes instead of the classic nix-channel rebuild method.

To get gohello in the system, first we need to add git to the commands available on the system in configuration.nix:

environment.systemPackages = with pkgs; [ git ];

Then we can add gohello to our system flake:

{
  inputs = {
    nixpkgs.url = "nixpkgs/nixos-unstable";
    # XXX(Xe): this URL may change for you, such as github:Xe/gohello-http
    gohello.url = "git+https://tulpa.dev/cadey/gohello-http?ref=main";
  };

  outputs = { self, nixpkgs, gohello, ... }: {
    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
        ./configuration.nix

        # add things here
        gohello.nixosModule
        ({ pkgs, ... }: {
          xeserv.services.gohello.enable = true;
        })
      ];
    };
  };
}

<Mara>

The block of code under gohello.nixosModule is an inline NixOS module. If we put gohello.nixosModule before the ./configuration.nix reference, we could put the xeserv.services.gohello.enable = true; line inside ./configuration.nix. This is an exercise for the reader.

And rebuild the system with gohello enabled:

sudo nixos-rebuild switch

Finally, poke it with curl:

$ curl http://gohello.local.cetacean.club
hello world :)

To update it, update the flake inputs in /etc/nixos and run nixos-rebuild:

sudo nix flake update /etc/nixos
sudo nixos-rebuild switch

And from here you can do whatever you want with NixOS. You can use containers, set up arbitrary services, or plan for world domination as normal.

<Numa>

I thought it was "to save the world from devastation", not "to plan for world domination". Who needs a monopoly on violence for world domination when you have Nix expressions?

<Cadey>

Siiiiiiiiiiiiiiiiiigh.

I will use this setup in future posts to make this more accessible and easy to hack at without having to have a dedicated NixOS machine laying around.

Facts and circumstances may have changed since publication. Please contact me before jumping to conclusions if something seems wrong or unclear.

Tags: nixos, wsl

Nix Flakes on WSL

Installation

Local Services

Installing gohello

Installing `gohello`