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How I use Nix to speed-up my development workflow

9 min read

Nix. A language, package manager, build tool, and an operating system. Reasoning about it can be tricky, but it’s a powerful tool to have in your toolbox, and it’s been at the core of my workflow for about two years now.

To preface what follows: I am not an expert and have only used a subset of the features of Nix. My primary goal started with wanting to version control my laptop config, to minimise the time it would take to get back online if something were to happen to my laptop. This journey led me to discover nix-flakes and how they could help quickstart development projects.

The natural question is: why not just use dotfiles / Homebrew? Although a good start, there are some issues with this approach. Well, various issues. I’ll try to enumerate them in no particular order.

  • The non-deterministic model of Homebrew. If I install a package today, and then try to install it again in 6 months, I might get a different version of the package, which could potentially break my workflow.

  • Homebrew pins packages to the latest versions. This means that if I want to use a specific version of a package, I have to manually install it and then pin it, which is a bit of a hassle.

  • Dotfiles are not portable enough. I run a few home servers on Linux, and I would have to maintain a separate set of dotfiles for my laptop (macOS) and my servers (Linux), which is not ideal.

I started looking for alternatives. My main requirements were:

  • Reproducibility. I want to be able to reproduce my development environment on any machine, at any time.
  • Portability. I want to be able to use the same configuration on my laptop and my servers.

This is how I stumbled upon Nix and it opened my eyes to what a purpose-built language for configuration could be. Not only can I control the applications and their versions that I’m installing, I can also control their configuration. This means that I can have a single source of truth for my development environment, and I can easily reproduce it on any machine.

Installing Nix

Installing Nix is not as straightforward as I might like, but the instructions on the official website are good enough. A few caveats to be aware of:

  • Nix is not available on Windows, so if you’re a Windows user, you’re out of luck. However, you can use WSL to run Nix on Windows.

  • Nix runs natively on macOS, but managing system-level settings the way you would on NixOS requires the nix-darwin project.

  • Nix likes to take over your system. I have been running Nix on my laptop for the past two years without any issues, so it’s not a deal breaker. However, it’s something to be aware of before you install Nix, especially if you’re running it in an enterprise environment where you might not have full control over your machine.

  • Nix uses a lot of disk space. Nix stores all of its packages in a single directory, which can take up a lot of disk space. However, you can use the nix-collect-garbage command to clean up old packages and free up disk space.

Nix on macOS

My daily driver is a MacBook Pro, so from the start I wanted to get Nix running on macOS — and this is where nix-darwin comes in. nix-darwin lets you manage your macOS system configuration with Nix, giving you a single source of truth that you can reproduce on any machine.

Nix-Darwin & Home Manager

The easiest way to think about this: nix-darwin manages system-level programs and configuration, while home-manager manages user configuration.

Example nix-darwin configuration:

# darwin.nix

{ pkgs, ... }: {
  # Enable flakes and optimize storage to save space
  nix.settings = {
    experimental-features = [ "nix-command" "flakes" ];
    auto-optimise-store = true;
  };

  # User Configuration
  users.users.robert = {
    name = "robert";
    home = "/Users/robert";
  };

  # 3. System Packages
  # Essential command line tools
  environment.systemPackages = with pkgs; [
    git
    neovim
    tmux
    ## Add more packages as needed
  ];

  # Create /etc/zshrc that loads the nix-darwin environment
  programs.zsh.enable = true;

  # MacOS System Preferences
  system.defaults = {
    # Keyboard settings
    NSGlobalDomain.KeyRepeat = 2;
    NSGlobalDomain.InitialKeyRepeat = 15;

    # Visual settings (Dock, Finder)
    dock.autohide = true;
    dock.show-recents = false;
    finder.AppleShowAllFiles = true;
  };

  # Keyboard remapping (CapsLock -> Escape)
  system.keyboard.enableKeyMapping = true;
  system.keyboard.remapCapsLockToEscape = true;

  # Use TouchID for `sudo` commands
  security.pam.services.sudo_local.touchIdAuth = true;
}

As we can see, there are already a lot of things going on in this configuration: from installing CLI tools, to remapping keys, to enabling Touch ID for sudo, and more. Although a small example of why Nix is so powerful, it’s just the beginning.

# home-manager.nix

{ config, pkgs, ... }:

{
  # Home Manager needs a bit of information about you and the paths it should manage.
  home.username = "robert";
  home.homeDirectory = "/home/robert";

  home.stateVersion = "24.05"; # Please update to your actual install version

  # 1. Install Packages "brew layer"
  # These are tools that don't need complex configuration, just the binary.
  home.packages = with pkgs; [
    # Modern CLI replacements
    eza      # Better 'ls'
    ripgrep  # Better 'grep'
    fd       # Better 'find'
    jq       # JSON processor
  ];

  # Configure Programs (The "Dotfiles" layer)
  programs = {
    home-manager.enable = true;

    # Git: Setup user identity and aliases
    git = {
      enable = true;
      userName = "robalaban";
      userEmail = "<[email protected]>";
      extraConfig = {
        init.defaultBranch = "main";
        pull.rebase = true;
      };
    };

    # Starship: A cross-shell prompt
    starship = {
      enable = true;
      settings = {
        add_newline = false;
        aws.disabled = true;
      };
    };

    # FZF: Fuzzy finder
    fzf = {
      enable = true;
      enableZshIntegration = true;
    };
  };
}

Now things are a little clearer: darwin.nix installs zsh / tmux, and home-manager.nix installs the packages that I want to use and configures them.

Nix Flakes

A modern way to manage your Nix configuration is to use Nix Flakes. Nix Flakes are a feature in Nix that lets you manage your configuration using a single file. This file is called flake.nix, and it contains all of the information about your Nix configuration, including the packages you want to install, the configuration for those packages, and any other information that you want to include.

The benefits of using flakes are that alongside the flake.nix file, you also get a flake.lock file which contains the exact versions of the packages that you’re using. This means that you can easily reproduce your Nix configuration on any machine, at any time, and you can be sure that you’re using the same versions of the packages.

Discovering flakes was the “aha” moment for me. Apart from making me realise that I had been using Nix in a suboptimal way before, I quickly realised that with flakes I could package not only my laptop configuration, but also the configuration for the various projects that I was working on. This meant that I could have a single source of truth for my entire development environment, and I could easily reproduce it on any machine.

The anatomy of a flake

{
  description = "Python development environment with uv package manager";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    flake-parts = {
      url = "github:hercules-ci/flake-parts";
      inputs.nixpkgs-lib.follows = "nixpkgs";
    };
  };

  outputs = inputs:
    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];

      perSystem = { pkgs, ... }:
        let
          # Use the latest stable Python version
          python = pkgs.python312;

          # Create a Python environment with common packages
          pythonEnv = python.withPackages (ps: with ps; [
            # Data science and scientific computing
            numpy
            pandas
            matplotlib

            # Web development
            requests
            flask
            fastapi

            # Development tools
            pytest
            black
            isort
            mypy
          ]);
        in
        {
          packages = {
            default = pythonEnv;
          };

          devShells = {
            default = pkgs.mkShell {
              packages = with pkgs; [
                pythonEnv

                # Modern Python package manager and tools
                uv # Fast Python package installer
                ruff # Fast Python linter
                pyright # Python language server
              ];
            };
          };

          apps = {
            default = {
              program = "${pythonEnv}/bin/python";
              type = "app";
            };
          };
        };
    };
}

This flake defines a portable Python development setup that I can enter or run consistently across Linux and macOS systems.

For the first time, I can install specific versions of Python and its packages, and be confident that the same environment will be reproduced on any machine. I can add any other required tools to the devShells section, and they will be available whenever I enter the development shell. As someone who juggles a few projects at the same time, in different languages, with different dependencies and tools, this workflow has been very ergonomic.

Conclusion

Flakes are where my discovery of Nix paused for now, and they have been a game changer for my development workflow. They have not only helped me with my primary goal of managing my laptop configuration, but also with managing the configuration for my various projects.

To see how I use flakes to manage my laptop configuration, check out my GitHub repository: config. If you want to see how I use flakes to manage my project configurations, check out my GitHub repository: frosted-flakes.

Resources

  • Nix Pills - A great tutorial series to get started with Nix.
  • Zero-to-Nix - Another great tutorial series to get started with Nix.