Building a Hugo site with Nix


So when the time came to rebuild this blog with Hugo, I knew it was probably a good excuse to learn how to use Nix for more general-purpose tasks, like generating a static site with a generator. There were some bumps along the way, but for the most part, having my builds be declarative & reproducible was a good idea, I think.

It all starts out with a Hugo site. If you’ve not got one, they have a great guide for that. Once you have that, you can move on to configuring a Nix flake. All I did to start with (while I figured my way around the Hugo CLI) was set up a dev shell.

{
  inputs.nixpkgs.url = "github:nixos/nixpkgs/release-23.11";

  outputs = inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      systems = inputs.nixpkgs.lib.systems.flakeExposed;

      perSystem = { self', pkgs, ... }:
        let
          inherit (pkgs) just hugo jq;
        in
        {
          devShells.default = pkgs.mkShell {
            buildInputs = [ just jq hugo ];
          };
        };
    };
}

This let me run nix develop to drop into a pre-configured shell with just, jq, and hugo installed. Ignoring the other two packages, we’re gonna be using hugo here to quickly test out our site.

$ hugo serve
...
Web Server is available at http://localhost:1313/ (bind address 127.0.0.1)
Press Ctrl+C to stop

Cool, so our site works. Now, what I could do is just blindly use GitHub’s template for building sites, but being the tinkerer I am, that wasn’t the best I could do. So what I did was dig into the way that Nixpkgs’s runCommand util worked. It seemed to do what I wanted, it lets you run a series of commands and populate a path at the variable $out with a file or directory to be persisted in the Nix store. So I set about doing that.

I knew that Hugo sets up some in-situ directories to track build state (things like lockfiles, pre-compiled static assets, etc.), so I was going to need a temporary working directory to run all this in. I also knew that I would need to probably call it with the --minify flag to be relatively performant.

All said, here’s what I landed on, putting it in my perSystem block in my flake:

{ pkgs, ... }: {
    ...
    packages = {
      default = pkgs.runCommand "dist" {
        src = ./.;
        buildInputs = [ hugo ];
      } ''
        work=$(mktemp -d)
        cp -r $src/* $work
        (cd $work && hugo --minify)
        cp -r $work/public $out
        rm -rf $work
      '';
    };
}

So what we’ve got here is runCommand, creating an output in the store called dist, taking the current directory (i.e. where both my flake and Hugo site root are) as a source input, and configuring hugo to be available in the build’s PATH.

Then, we’re giving it a multi-line string which is pretty much equivalent to a bash script in this instance. We create a temporary working directory (which we store the path to in a variable called work), make a copy of our sources there, and then run hugo --minify from that folder to build our site fully. With that done, we can finally copy the contents of the public/ directory to the $out path in the Nix store.

All this comes together to give us a path on the nix store (/nix/store/<hash>-dist/) with our fully-built and ready-to-deploy website.

Nice. So we build this with nix build .#default, and we get the contents of our would-be public/ dir in a symlink to the Nix store path called result.

Note: If you want to run this with symlinked themes in your themes/ dir like me, you need to build .?submodules=1#default, not just .#default. This is because Nix ignores submodules in Flakes for some reason unless you explicitly tell it to use them.

$ ls -lah result
Permissions Size User Date Modified Name
.r--r--r--  3.0k root  1 Jan  1970 404.html
.r--r--r--   65k root  1 Jan  1970 android-chrome-192x192.png
.r--r--r--  336k root  1 Jan  1970 android-chrome-512x512.png
.r--r--r--   59k root  1 Jan  1970 apple-touch-icon.png
dr-xr-xr-x     - root  1 Jan  1970 categories
dr-xr-xr-x     - root  1 Jan  1970 css
.r--r--r--   987 root  1 Jan  1970 favicon-16x16.png
.r--r--r--  3.0k root  1 Jan  1970 favicon-32x32.png
.r--r--r--   15k root  1 Jan  1970 favicon.ico
dr-xr-xr-x     - root  1 Jan  1970 images
.r--r--r--  3.9k root  1 Jan  1970 index.html
.r--r--r--  1.9k root  1 Jan  1970  󰗀 index.xml
dr-xr-xr-x     - root  1 Jan  1970 posts
.r--r--r--   672 root  1 Jan  1970  󰗀 sitemap.xml
dr-xr-xr-x     - root  1 Jan  1970 tags

(I’m using eza as an ls replacement, hence the weird formatting)

Cool. So now, I can run a Nix build in GitHub actions and zip up the contents of public using their actions/upload-pages-artifact@v2 action, and deploy it to Pages like it was any other tool :)

All in all, I’m not sure using Nix for this provides much raw benefit over just using a normal CD pipeline to do this (i.e. using their template), but it was fun to set up and simplifies being able to run this on any machine I want to work on it from.

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blog of a lowly devops engineer from the uk, hoping to maybe make you laugh sometimes


How I learned to build up a Hugo site using Nix.

(Source)