private String processRackInfo(Map<String, Object> properties) {
    String rackInfo = null;
    if (properties.containsKey(HostResourceProvider.HOST_RACK_INFO_PROPERTY_ID)) {
      rackInfo = (String) properties.get(HostResourceProvider.HOST_RACK_INFO_PROPERTY_ID);
    } else if (properties.containsKey(HostResourceProvider.RACK_INFO_PROPERTY_ID)) {
      rackInfo = (String) properties.get(HostResourceProvider.RACK_INFO_PROPERTY_ID);
    } else {
      LOGGER.debug("No rack info provided");
    }
    return rackInfo;
  }
Parse and set host group information.

@param properties  request properties
@throws InvalidTopologyTemplateException if any property validation fails
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/ScaleClusterRequest.java