@Transactional
  void mapHostClusterEntities(String hostName, Long clusterId) {
    HostEntity hostEntity = hostDAO.findByName(hostName);
    ClusterEntity clusterEntity = clusterDAO.findById(clusterId);

    hostEntity.getClusterEntities().add(clusterEntity);
    clusterEntity.getHostEntities().add(hostEntity);

    clusterDAO.merge(clusterEntity);
    hostDAO.merge(hostEntity);
  }
Attempts to map the host to the cluster via clusterhostmapping table if not already present, and add a host_version
record for the cluster's currently applied (stack, version) if not already present.
@param hostname Host name
@param clusterName Cluster name
@throws AmbariException May throw a DuplicateResourceException.
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClustersImpl.java