{
  description = "system flake.nix";
  inputs = {
    sops-nix.url = "github:Mic92/sops-nix";
    nixpkgs.url = "github:nixos/nixpkgs/nixos-21.05";
    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
    polygon-art = {
      url = "git+https://git.ingolf-wagner.de/palo/polygon-art.git";
      #inputs.nixpkgs.follows = "nixpkgs";
    };
    doom-emacs-nix = {
      url = "github:vlaci/nix-doom-emacs";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    home-manager = {
      url = "github:nix-community/home-manager/release-21.05";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    home-manager-utils = {
      url = "github:mrvandalo/home-manager-utils";
      inputs.home-manager.follows = "home-manager";
    };
    backup-module = {
      url = "git+https://git.ingolf-wagner.de/nix-modules/backup.git";
      flake = false;
    };
    krops-lib = {
      url = "git+https://git.ingolf-wagner.de/nix-modules/krops.git";
      flake = false;
    };
    cluster-module = {
      url =
        "git+https://git.ingolf-wagner.de/nix-modules/cluster.git?rev=ef621797a30f8a57de16bf33672abdd411cbcece";
      flake = false;
    };
  };

  outputs = { self, sops-nix, nixpkgs, home-manager, home-manager-utils
    , doom-emacs-nix, backup-module, nixpkgs-unstable, krops-lib, cluster-module
    , polygon-art, ... }:

    let
      nixosSystem = nixpkgs.lib.nixosSystem;
      defaultModules = [
        sops-nix.nixosModules.sops
        { imports = [ "${krops-lib}" "${cluster-module}" "${backup-module}" ]; }
        ({ pkgs, ... }: {
          nix = {
            # no channesl needed this way
            nixPath = [ "nixpkgs=${pkgs.path}" ];
            # make flakes available
            package = pkgs.nixUnstable;
            extraOptions = ''
              experimental-features = nix-command flakes
            '';
          };
          # defined overlays injected by the nixflake
          nixpkgs.overlays = [
            (_self: _super: {
              # we assign the overlay created before to the overlays of nixpkgs.
              unstable = nixpkgs-unstable.legacyPackages.${pkgs.system};
              polygon-art = polygon-art.packages.${pkgs.system};
            })
          ];
        })
        home-manager.nixosModules.home-manager
        {
          home-manager.useGlobalPkgs = true;
          home-manager.useUserPackages = true;
        }
      ];
      desktopModules = [
        home-manager.nixosModules.home-manager
        {
          home-manager.users.mainUser = {
            imports = [ doom-emacs-nix.hmModule home-manager-utils.hmModule ];
          };
          home-manager.useGlobalPkgs = true;
          home-manager.useUserPackages = true;
        }
      ];
      desktopConfiguration = initPath:
        nixosSystem {
          system = "x86_64-linux";
          modules = defaultModules ++ desktopModules ++ [ initPath ];
        };
      serverConfiguration = initPath:
        nixosSystem {
          system = "x86_64-linux";
          modules = defaultModules ++ [ initPath ];
        };
    in {
      nixosConfigurations = {
        sterni = desktopConfiguration ./configs/sterni/configuration.nix;
        sternchen = desktopConfiguration ./configs/sternchien/configuration.nix;
        pepe = serverConfiguration ./configs/pepe/configuration.nix;
        workhorse = serverConfiguration ./configs/workhorse/configuration.nix;
        sputnik = serverConfiguration ./configs/sputnik/configuration.nix;
      };
    };
}