anchor.diff:  
       ddUrl = mkOption {
         description = ''
  -        Custom dd_url to configure the agent with.
  -        Useful when you want to point datadog to another endpoint, either
  -        because you need a proxy to send out data, or because you use their EU
  -        endpoint.
  -      '';
  -      default = "https://app.datadoghq.com";
  -      example = "https://app.datadoghq.eu";
  -      type = types.str;
  +        Custom dd_url to configure the agent with. Useful if traffic to datadog
  +        needs to go through a proxy.
  +        Don't use this to point to another datadog site (EU) - use site instead.
  +      '';
  +      default = null;
  +      example = "http://haproxy.example.com:3834";
  +      type = types.nullOr types.str;
  +    };
  +
  +    site = mkOption {
  +      description = ''
  +        The datadog site to point the agent towards.
  +        Set to datadoghq.eu to point it to their EU site.
  +      '';
  +      default = null;
  +      example = "datadoghq.eu";
  +      type = types.nullOr types.str;
       };
   
       tags = mkOption {
  
positive.code:   cfg = config.services.datadog-agent;
  
    ddConf = {
      dd_url              = cfg.ddUrl;
      skip_ssl_validation = false;
      confd_path          = "/etc/datadog-agent/conf.d";
      additional_checksd  = "/etc/datadog-agent/checks.d";
  
negative.code:   }
    // optionalAttrs (cfg.logLevel != null) { log_level = cfg.logLevel; }
    // optionalAttrs (cfg.hostname != null) { inherit (cfg) hostname; }
    // optionalAttrs (cfg.ddUrl != null) { dd_url = cfg.ddUrl; }
    // optionalAttrs (cfg.site != null) { site = cfg.site; }
    // optionalAttrs (cfg.tags != null ) { tags = concatStringsSep ", " cfg.tags; }
    // optionalAttrs (cfg.enableLiveProcessCollection) { process_config = { enabled = "true"; }; }
    // optionalAttrs (cfg.enableTraceAgent) { apm_config = { enabled = true; }; }
  