@Override
  public List<ServiceComponentHost> getServiceComponentHosts(String hostname) {
    List<ServiceComponentHost> serviceComponentHosts = serviceComponentHostsByHost.get(hostname);
    if (null != serviceComponentHosts) {
      return new CopyOnWriteArrayList<>(serviceComponentHosts);
    }

    return new ArrayList<>();
  }
Make sure we load all the service host components.
We need this for live status checks.
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClusterImpl.java