public ServiceComponentHost getServiceComponentHost(String serviceName,
      String serviceComponentName, String hostname) throws AmbariException {
    if (!serviceComponentHosts.containsKey(serviceName)
        || !serviceComponentHosts.get(serviceName).containsKey(
            serviceComponentName)
        || !serviceComponentHosts.get(serviceName).get(serviceComponentName).containsKey(
            hostname)) {
      throw new ServiceComponentHostNotFoundException(getClusterName(),
          serviceName, serviceComponentName, hostname);
    }
    return serviceComponentHosts.get(serviceName).get(serviceComponentName).get(hostname);
  }
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