newtype-org-configurations/modules/hosts.nix

{ lib, config, ... }:
let
  hostOptions = with lib; {
    ipv4 = mkOption {
      default = null;
      type = types.nullOr types.str;
      description = ''
        own ipv4 address
      '';
    };

    ipv6 = mkOption {
      type = types.nullOr types.str;
      default = null;
      description = ''
        own ipv6 address
      '';
    };
  };
in
{
  options = with lib; {
    networking.newtype.hosts = mkOption {
      type = with types; attrsOf (submodule [{ options = hostOptions; }]);
      description = "A host in our cluster";
    };
    networking.newtype.currentHost = mkOption {
      type = with types; submodule [{ options = hostOptions; }];
      default = config.networking.newtype.hosts.${config.networking.hostName};
      description = "The host that is described by this configuration";
    };
  };
  config = {
    warnings =
      lib.optional (!(config.networking.newtype.hosts ? ${config.networking.hostName}) && 
        config.networking.hostName != "nixos" # we dont care about nixos netboot/installer images
      )
        "Please add network configuration for ${config.networking.hostName}. None found in ${./hosts.nix}";

    # usually, for each host there is a hostname.dse.in.tum.de and hostname.r domain
    networking.newtype.hosts = {
      epyc = {
        ipv6 = "2001:bc8:38ee:100::500";
      };
    };
  };
}