private Map<String, Set<String>> gatherHostGroupBindings(ClusterTopology clusterTopology) {
    Map<String, Set<String>> hgBindngs = Maps.newHashMap();
    for (Map.Entry<String, HostGroupInfo> hgEnrty: clusterTopology.getHostGroupInfo().entrySet()) {
      hgBindngs.put(hgEnrty.getKey(), Sets.newCopyOnWriteArraySet(hgEnrty.getValue().getHostNames()));
    }
    return hgBindngs;
  }
Recommend configurations by the stack advisor, then store the results in cluster topology.
@param clusterTopology cluster topology instance
@param userProvidedConfigurations User configurations of cluster provided in Blueprint + Cluster template
ambari-server/src/main/java/org/apache/ambari/server/api/services/stackadvisor/StackAdvisorBlueprintProcessor.java