cryodev/AGENTS.md

Agent Guidelines for NixOS Configuration

Project Overview

This repository contains a NixOS configuration managed with Nix Flakes. It defines:

• Hosts: cryodev-main (x86_64 server), cryodev-pi (aarch64 Raspberry Pi)
• Modules: Reusable NixOS modules in modules/nixos/
• Packages: Custom packages in pkgs/
• Templates: raspberry-pi, generic-server for bootstrapping new hosts

Build & Development Commands

Prerequisites

• Nix with Flakes enabled
• Git

Core Commands

# Build host configuration
nix build .#nixosConfigurations.cryodev-main.config.system.build.toplevel
nix build .#nixosConfigurations.cryodev-pi.config.system.build.toplevel

# Build Raspberry Pi SD image (requires binfmt on x86_64)
nix build .#nixosConfigurations.cryodev-pi.config.system.build.sdImage

# Format code (required before committing)
nix fmt

# Run all checks (lint, formatting, deploy-rs validation)
nix flake check

# Quick evaluation test (faster than full build)
nix eval .#nixosConfigurations.cryodev-main.config.system.build.toplevel.name

# Update flake inputs
nix flake update

# Enter development shell
nix develop

Deployment

# Deploy to cryodev-main via deploy-rs
nix run github:serokell/deploy-rs -- .#cryodev-main

# Manual deployment via SSH
nixos-rebuild switch --flake .#<hostname> \
  --target-host <user>@<ip> --use-remote-sudo \
  --ssh-option="-p 2299"

Code Style & Conventions

Formatting

• Tool: nixfmt via pre-commit hooks
• Run: nix fmt before every commit
• Indentation: 2 spaces
• Line length: 80-100 characters (follow formatter)

Module Structure

# Standard module pattern
{ config, lib, pkgs, inputs, outputs, constants, ... }:

let
  cfg = config.services.myService;
in
{
  options.services.myService = {
    enable = lib.mkEnableOption "My service";
    port = lib.mkOption {
      type = lib.types.port;
      default = 8080;
      description = "Port to listen on";
    };
  };

  config = lib.mkIf cfg.enable {
    # Implementation here
  };
}

Naming Conventions

Type	Convention	Example
Files	kebab-case	hardware-configuration.nix
Options	camelCase	services.myService.enable
Variables	camelCase	let myValue = ...;
Hosts	kebab-case	cryodev-main, cryodev-pi

Imports

# Local modules: relative paths
imports = [ ./hardware.nix ./networking.nix ];

# Shared modules: via outputs
imports = [ outputs.nixosModules.common ];

# External inputs
imports = [ inputs.sops-nix.nixosModules.sops ];

Constants

Use constants.nix for domains, IPs, and ports:

{ constants, ... }:
{
  services.nginx.virtualHosts."${constants.services.forgejo.fqdn}" = { ... };
}

Error Handling

config = lib.mkIf cfg.enable {
  assertions = [
    { assertion = cfg.port > 1024; message = "Port must be > 1024"; }
  ];
  warnings = lib.optional (cfg.debug) "Debug mode enabled!";
};

Option Conflicts

Use lib.mkDefault for default values that can be overridden:

services.nginx.enable = lib.mkDefault true;

Directory Structure

.
├── flake.nix              # Entry point, inputs/outputs
├── constants.nix          # Central config (domains, IPs, ports)
├── hosts/
│   ├── cryodev-main/      # x86_64 server
│   │   ├── default.nix    # Host entry point
│   │   ├── hardware.nix   # Hardware configuration
│   │   ├── services/      # Service configurations
│   │   └── secrets.yaml   # SOPS-encrypted secrets
│   └── cryodev-pi/        # aarch64 Raspberry Pi
├── modules/nixos/         # Reusable modules
│   ├── common/            # Shared base configuration
│   ├── sops/              # Secret management
│   ├── forgejo/           # Git server
│   ├── headscale/         # VPN control server
│   └── ...
├── lib/utils.nix          # Helper functions
├── apps/                  # Nix apps (rebuild)
├── pkgs/                  # Custom packages
├── overlays/              # Nixpkgs overlays
├── templates/             # Host templates
├── scripts/               # Helper scripts (install.sh)
└── docs/                  # Documentation

Key Patterns

Adding a New Raspberry Pi Host

1. Copy template: cp -r templates/raspberry-pi hosts/new-pi
2. Update hosts/new-pi/networking.nix (hostname)
3. Add to flake.nix: new-pi = mkNixosConfiguration "aarch64-linux" [ ./hosts/new-pi ];
4. Add to .forgejo/workflows/build-pi-image.yml matrix
5. Push → SD image is built automatically

SOPS Secrets

• Secrets encrypted with age using SSH host keys
• Config in .sops.yaml, secrets in hosts/<host>/secrets.yaml
• Reference: config.sops.secrets."path/to/secret".path

Special Args Available in Modules

• inputs: Flake inputs (nixpkgs, sops-nix, etc.)
• outputs: This flake's outputs (nixosModules, packages)
• constants: Values from constants.nix
• lib: Extended nixpkgs.lib with lib.utils

Deployment Workflows

Host	Strategy	Trigger
cryodev-main	Push via deploy-rs	Forgejo Actions on push to main
cryodev-pi	Pull via Comin	Automatic polling
SD Images	Built in CI	Push to main (for Pi hosts)

Verification Checklist

Before committing:

• nix fmt passes
• nix flake check passes (or at least nix eval works)
• New hosts added to flake.nix
• Constants in constants.nix, not hardcoded
• Secrets use SOPS, not plaintext