Clean NixOS: From configuration.nix to Dendritic

Hey there! I'm writing this blog since I found that it's nearly impossible to find proper resources on NixOS and how to structure your configuration properly. Instead of forcing you to figure everything out yourself, here's an easy way to modularize your NixOS configuration and make it cleaner overall.

0. The Dendritic Paradigm 

What the hell is a Dendritic? Well, in short, it's a paradigm that flips the configuration matrix from device-centric to feature-centric. I layman's terms, it's a way of writing Nix code that makes your configuration stay clean as it scales, and avoid the headache of imports and weird, nested folder structures.

1. From configuration.nix to a Dendritic-ish Flake

I'll start from a clean NixOS install, though please don't skip this part even if you already have your config in a flake. After installing, my /etc/nixos/configuration.nix file looks as follows:

Yours should be similar enough to this... If you don't know what an option does, feel free to look it up by running man configuration.nix in another shell. The first thing we want to do here is to turn this from a configuration.nix into a flake.

Create a new file called flake.nix, and copy the following code into it:

Let's break down the inputs:

1. a pinned version of Nixpkgs
2. a library called Flake Parts, that will later help us define modules
3. a library called Import Tree, that will kill the hydra that is bad folder structuring
4. a library called Systems, which is unfortunately part of the boilerplate

Alas! The boilerplate introduced by this paradigm will be much smaller than the boilerplate that you'd be writing otherwise.

For the outputs, you're basically defining a Flake Parts output... feel free to read up on the Flake Parts wiki for more details, since I don't really understand it myself. In the imports, after importing some Flake Parts helper functions that you can ignore, two sets of files are imported. First, ./hosts.nix is imported, where we will go on to define any and all devices we want to make a configuration for. Second, (inputs.import-tree ./modules) imports every file within the modules folder, where we will be migrating the bulk of our configuration to (you can keep this line commented for now).

Also, let's already define the hosts.nix file as follows:

Now run sudo nixos-rebuild --flake <folder-directory>#default switch command, where you can replace <folder-directory> placeholder with your actual folder name (this means you can feel free to move your folder into the home directory now, so you don't need to run sudo for everything).

If you copied everything down correctly, it should compile! If it doesn't, please double check your code or write me a comment. Phew! Feel free to take a break here, you should be able to keep using your configuration.nix as usual.

2. Defining aspects, modularizing your code

Now it's finally time to break your code up into modules! Let's start by uncommenting that line in the flake.nix that we left commented earlier: