@Override
  public String getHealthyHost(Set<String> hostList) throws AmbariException {
    List<String> healthyHosts = selectHealthyHosts(hostList);

    if (!healthyHosts.isEmpty()) {
      Collections.shuffle(healthyHosts);
      return healthyHosts.get(0);
    }

    return null;
  }
Chooses a healthy host from the list of candidate hosts randomly. If there
are no healthy hosts, then this method will return {@code null}.
<p/>
The host's {@link HostState} is used to determine if a host is healthy.

@return a random healthy host, or {@code null}.
@throws AmbariException
@see {@link HostState#HEALTHY}
ambari-server/src/main/java/org/apache/ambari/server/controller/AmbariManagementControllerImpl.java