private String getATSUrlFromCustom() {
    String atsUrl = context.getProperties().get(YARN_ATS_URL);
    if (!StringUtils.isEmpty(atsUrl)) {
      if (!hasProtocol(atsUrl)) {
        throw new AmbariApiException(
          "RA070 View is not cluster associated. Timeline Server URL should contain protocol.");
      }
      return atsUrl;
    } else {
      throw new AmbariApiException(
        "RA070 View is not cluster associated. 'YARN Timeline Server URL' should be provided");
    }
  }
@return The timeline server url. If the view instance is cluster associated, the value is taken from the
yarn-site.xml else it is retrieved from the view configuration.
contrib/views/utils/src/main/java/org/apache/ambari/view/utils/ambari/Services.java