anchor.diff:        description = "Whether to enable elasticsearch.";
         default = false;
         type = types.bool;
  +    };
  +
  +    package = mkOption {
  +      description = "Elasticsearch package to use.";
  +      default = pkgs.elasticsearch;
  +      type = types.package;
       };
   
       host = mkOption {
  
positive.code:       after = [ "network-interfaces.target" ];
        environment = { ES_HOME = cfg.dataDir; };
        serviceConfig = {
          ExecStart = "${pkgs.elasticsearch}/bin/elasticsearch -Des.path.conf=${configDir} ${toString cfg.extraCmdLineOptions}";
          User = "elasticsearch";
          PermissionsStartOnly = true;
        };
  
negative.code:       '';
      };
  
      environment.systemPackages = [ cfg.package ];
  
      users.extraUsers = singleton {
        name = "elasticsearch";
  