Feature Flags

The problem

Enabling a capability often means configuring several services together. Doing that inline in each host file produces copy-paste, drift, and no way to validate that prerequisites are met.

The solution

Capabilities are exposed as typed feature flags under features.*. A host turns a dial; the module behind it wires up the actual services. The shared option declarations live in modules/common/features.nix, which groups them as development, virtualization, cloud, security, networking, ai, programs, media and quickshell. Individual services declare their own flag in their own module instead.

# In a host configuration.nix — declarative intent, not implementation
features = {
  development.enable = true;
  virtualization = {
    enable = true;
    docker = true;
  };
  ai.enable = true;
  media.enable = true;
  syncthing.enable = true;
};

How a feature module is shaped

Every module follows the same contract: declare options, then apply config only when enabled.

{ config, lib, pkgs, ... }:
let
  cfg = config.features.myservice;
in
{
  options.features.myservice = {
    enable = lib.mkEnableOption "MyService";
    port = lib.mkOption {
      type = lib.types.port;
      default = 8080;
      description = "Port MyService listens on.";
    };
  };

  config = lib.mkIf cfg.enable {
    services.myservice = {
      enable = true;
      port = cfg.port;
    };
  };
}

Never configure services directly in a host

services.foo = { … } in hosts/*/configuration.nix defeats reuse and testing. Wrap it in a module under modules/ and expose a feature flag. This is a hard rule — see Anti-Patterns.

Host types

There is no central registry of feature dependencies or conflicts, and no cross-feature validation pass — a module that needs a prerequisite asserts it itself, with assertions.

What does exist is lib/hostTypes.nix, which pre-composes flags for a role. Two types are defined:

Type	Sets
workstation	development, desktop, virtualization
laptop	development, desktop, virtualization (no Docker), powerManagement

Both are set with lib.mkDefault, so a host that assigns the flag directly always wins:

# hosts/razer/configuration.nix — overrides the laptop default
features.virtualization.docker = true;

Each host imports one type plus its own hardware configuration.

Browsing what exists

The full set of feature-flagged modules — every option, with its description and the source — is in the generated Modules reference.