nixos-configuration/modules/server.nix

{
  config,
  pkgs,
  lib,
  ...
}: let
  cfg = config.my.server;
in {
  options.my.server = {
    enable = lib.mkEnableOption "server role";
  };

  config = lib.mkIf cfg.enable {
    networking.firewall = {
      enable = true;
      allowedTCPPortRanges = [
      ];
    };
  };
}