private RequestStatusResponse submitHostRequests(Request request) throws SystemException {
    ScaleClusterRequest requestRequest;
    try {
      requestRequest = new ScaleClusterRequest(request.getProperties());
    } catch (InvalidTopologyTemplateException e) {
      throw new IllegalArgumentException("Invalid Add Hosts Template: " + e, e);
    }

    try {
      return topologyManager.scaleHosts(requestRequest);
    } catch (InvalidTopologyException e) {
      throw new IllegalArgumentException("Topology validation failed: " + e, e);
    } catch (AmbariException e) {
      //todo: handle non-system exceptions
      e.printStackTrace();
      //todo: for now just throw SystemException
      throw new SystemException("Unable to add hosts", e);
    }
  }
Obtain the hostname from the request properties.  The hostname property name may differ
depending on the request type.  For the low level host resource creation calls, it is always
"Hosts/host_name".  For multi host "add host from hostgroup", the hostname property is a top level
property "host_name".

@param properties  request properties

@return the host name for the host request
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/HostResourceProvider.java