protected List<ChangedConfigInfo> calculateChangedConfigurations(Request request) {
    List<ChangedConfigInfo> configs =
      new LinkedList<>();
    HashSet<HashMap<String, String>> changedConfigs =
      (HashSet<HashMap<String, String>>) getRequestProperty(request, CHANGED_CONFIGURATIONS_PROPERTY);
    for (HashMap<String, String> props: changedConfigs) {
      configs.add(new ChangedConfigInfo(props.get("type"), props.get("name"), props.get("old_value")));
    }

    return configs;
  }
Retrieves hosts names mapped by host groups, host name is used as host group identifier
@param cluster cluster for calculating hosts mapping by host groups
@return map "host group name" -> ["host name 1"]
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/StackAdvisorResourceProvider.java