{
  description = "NixOS Base Image";

  inputs = {
    # nixpkgs repo for system packages
    nixpkgs.url = "github:nixos/nixpkgs";
    # nixos-generators lets us produce a "proxmox"-formatted image
    nixos-generators = {
      url = "github:nix-community/nixos-generators";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, nixos-generators,... }:
    {
      packages.x86_64-linux = {
        base = nixos-generators.nixosGenerate {
          system = "x86_64-linux";
          modules = [
            {
              # Pin nixpkgs to the flake input, so that the packages installed
              # come from the flake inputs.nixpkgs.url.
              nix.registry.nixpkgs.flake = nixpkgs;
              # set disk size to to 20G
              # virtualisation.diskSize = 20 * 1024;
            }
            ./configuration.nix
          ];
          format  = "proxmox";  # outputs a .vma.zst suitable for qmrestore
        };
      };
    };
}