{
  description = "CCCHH Nix Infrastructure";

  inputs = {
    # Use the NixOS small channels for nixpkgs.
    # https://nixos.org/manual/nixos/stable/#sec-upgrading
    # https://github.com/NixOS/nixpkgs
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05-small";
    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable-small";

    # Add nixos-generators as an input.
    # See here: https://github.com/nix-community/nixos-generators#using-in-a-flake
    nixos-generators = {
      url = "github:nix-community/nixos-generators";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { nixpkgs, nixpkgs-unstable, nixos-generators, ... }:
    let
      # Shairport Sync with metadata and MQTT support.
      shairportSyncExtendedNixpkgsUnstableOverlay = final: prev: {
        shairport-sync = (prev.shairport-sync.override { enableMetadata = true; }).overrideAttrs (finalAttr: previousAttr: {
          # See: https://github.com/mikebrady/shairport-sync/blob/e78a88b64adfe7b5f88fd6faedf55c57445bb240/CONFIGURATION%20FLAGS.md
          configureFlags = previousAttr.configureFlags ++ [ "--with-mqtt-client" ];
          buildInputs = previousAttr.buildInputs ++ [ final.mosquitto ];
        });
      };
    in {
    colmena = {
      meta = {
        nixpkgs = nixpkgs.legacyPackages."x86_64-linux";
        nodeNixpkgs = {
          audio = nixpkgs-unstable.legacyPackages."x86_64-linux".extend shairportSyncExtendedNixpkgsUnstableOverlay;
        };
      };

      audio = {
        deployment = {
          targetHost = "audio.z9.ccchh.net";
          targetPort = 22;
          targetUser = "colmena-deploy";
          tags = [ "thinkcccluster" ];
        };
        imports = [ 
          ./config/common
          ./config/proxmox-vm
          ./config/hosts/audio
        ];
      };

      public-reverse-proxy = {
        deployment = {
          targetHost = "public-reverse-proxy.z9.ccchh.net";
          targetPort = 22;
          targetUser = "colmena-deploy";
          tags = [ "thinkcccluster" ];
        };
        imports = [ 
          ./config/common
          ./config/proxmox-vm
          ./config/hosts/public-reverse-proxy
        ];
      };

      netbox = {
        deployment = {
          targetHost = "netbox-intern.hamburg.ccc.de";
          targetPort = 22;
          targetUser = "colmena-deploy";
          tags = [ "chaosknoten" ];
        };
        imports = [ 
          ./config/common
          ./config/proxmox-vm
          ./config/hosts/netbox
        ];
      };

      matrix = {
        deployment = {
          targetHost = "matrix-intern.hamburg.ccc.de";
          targetPort = 22;
          targetUser = "colmena-deploy";
          tags = [ "chaosknoten" ];
        };
        imports = [ 
          ./config/common
          ./config/proxmox-vm
          ./config/hosts/matrix
        ];
      };
    };

    packages.x86_64-linux = {
      proxmox-nixos-template = nixos-generators.nixosGenerate {
        system = "x86_64-linux";
        modules = [
          ./config/nixos-generators/proxmox.nix
          ./config/common
          ./config/proxmox-vm
        ];
        format = "proxmox";
      };

      proxmox-chaosknoten-nixos-template = nixos-generators.nixosGenerate {
        system = "x86_64-linux";
        modules = [
          ./config/nixos-generators/proxmox-chaosknoten.nix
          ./config/proxmox-chaosknoten-additional-initial-config.nix
          ./config/common
          ./config/proxmox-vm
        ];
        format = "proxmox";
      };
    };
  };
}