protected void deleteHosts(Set<HostRequest> requests) throws AmbariException {

    AmbariManagementController controller = getManagementController();
    Clusters clusters = controller.getClusters();

    List<HostRequest> okToRemove = new ArrayList<HostRequest>();

    for (HostRequest hostRequest : requests) {
      String hostName = hostRequest.getHostname();
      if (null == hostName) {
        continue;
      }

      Set<String> clusterNamesForHost = new HashSet<String>();
      if (null != hostRequest.getClusterName()) {
        clusterNamesForHost.add(hostRequest.getClusterName());
      } else {
        Set<Cluster> clustersForHost = clusters.getClustersForHost(hostRequest.getHostname());
        if (null != clustersForHost) {
          for (Cluster c : clustersForHost) {
            clusterNamesForHost.add(c.getClusterName());
          }
        }
      }

      for (String clusterName : clusterNamesForHost) {
        Cluster cluster = clusters.getCluster(clusterName);

        List<ServiceComponentHost> list = cluster.getServiceComponentHosts(hostName);

        if (!list.isEmpty()) {

          List<String> componentsToRemove = new ArrayList<String>();
          for (ServiceComponentHost sch : list) {
            Service s = cluster.getService(sch.getServiceName());
            ServiceComponent sc = s.getServiceComponent(sch.getServiceComponentName());

            // Masters and Slaves must be deleted first. Clients are ok.
            if (!sc.isClientComponent()) {
              componentsToRemove.add(sch.getServiceComponentName());
            }
          }

          if (!componentsToRemove.isEmpty()) {
            StringBuilder reason =
                new StringBuilder("Cannot remove host ")
                    .append(hostName)
                    .append(" from ")
                    .append(hostRequest.getClusterName())
                    .append(
                        ".  The following roles exist, and these components must be stopped if running, and then deleted: ");

            reason.append(StringUtils.join(componentsToRemove, ", "));

            throw new AmbariException(reason.toString());
          }
        }
      }
      okToRemove.add(hostRequest);
    }

    for (HostRequest hostRequest : okToRemove) {
      // Assume the user also wants to delete it entirely, including all clusters.
      clusters.deleteHost(hostRequest.getHostname());

      if (null != hostRequest.getClusterName()) {
        clusters.getCluster(hostRequest.getClusterName()).recalculateAllClusterVersionStates();
      }
    }
  }
  protected static Set<HostResponse> getHosts(
      AmbariManagementController controller, HostRequest request) throws AmbariException {

    // TODO/FIXME host can only belong to a single cluster so get host directly from Cluster
    // TODO/FIXME what is the requirement for filtering on host attributes?

    List<Host> hosts;
    Set<HostResponse> response = new HashSet<HostResponse>();
    Cluster cluster = null;

    Clusters clusters = controller.getClusters();

    String clusterName = request.getClusterName();
    String hostName = request.getHostname();

    if (clusterName != null) {
      // validate that cluster exists, throws exception if it doesn't.
      try {
        cluster = clusters.getCluster(clusterName);
      } catch (ObjectNotFoundException e) {
        throw new ParentObjectNotFoundException("Parent Cluster resource doesn't exist", e);
      }
    }

    if (hostName == null) {
      hosts = clusters.getHosts();
    } else {
      hosts = new ArrayList<Host>();
      try {
        hosts.add(clusters.getHost(request.getHostname()));
      } catch (HostNotFoundException e) {
        // add cluster name
        throw new HostNotFoundException(clusterName, hostName);
      }
    }

    for (Host h : hosts) {
      if (clusterName != null) {
        if (clusters.getClustersForHost(h.getHostName()).contains(cluster)) {
          HostResponse r = h.convertToResponse();

          r.setClusterName(clusterName);
          r.setDesiredHostConfigs(h.getDesiredHostConfigs(cluster));
          r.setMaintenanceState(h.getMaintenanceState(cluster.getClusterId()));

          response.add(r);
        } else if (hostName != null) {
          throw new HostNotFoundException(clusterName, hostName);
        }
      } else {
        HostResponse r = h.convertToResponse();

        Set<Cluster> clustersForHost = clusters.getClustersForHost(h.getHostName());
        // todo: host can only belong to a single cluster
        if (clustersForHost != null && clustersForHost.size() != 0) {
          r.setClusterName(clustersForHost.iterator().next().getClusterName());
        }
        response.add(r);
      }
    }
    return response;
  }
  protected synchronized void updateHosts(Set<HostRequest> requests) throws AmbariException {

    if (requests.isEmpty()) {
      LOG.warn("Received an empty requests set");
      return;
    }

    AmbariManagementController controller = getManagementController();
    Clusters clusters = controller.getClusters();

    for (HostRequest request : requests) {
      if (request.getHostname() == null || request.getHostname().isEmpty()) {
        throw new IllegalArgumentException("Invalid arguments, hostname should be provided");
      }
    }

    for (HostRequest request : requests) {
      if (LOG.isDebugEnabled()) {
        LOG.debug(
            "Received an updateHost request"
                + ", hostname="
                + request.getHostname()
                + ", request="
                + request);
      }

      Host host = clusters.getHost(request.getHostname());

      String clusterName = request.getClusterName();

      try {
        // The below method call throws an exception when trying to create a duplicate mapping in
        // the clusterhostmapping
        // table. This is done to detect duplicates during host create. In order to be robust,
        // handle these gracefully.
        clusters.mapHostToCluster(request.getHostname(), clusterName);
      } catch (DuplicateResourceException e) {
        // do nothing
      }

      if (null != request.getHostAttributes()) {
        host.setHostAttributes(request.getHostAttributes());
      }

      String rackInfo = host.getRackInfo();
      String requestRackInfo = request.getRackInfo();
      boolean rackChange = requestRackInfo != null && !requestRackInfo.equals(rackInfo);

      if (rackChange) {
        host.setRackInfo(requestRackInfo);
      }

      if (null != request.getPublicHostName()) {
        host.setPublicHostName(request.getPublicHostName());
      }

      if (null != clusterName && null != request.getMaintenanceState()) {
        Cluster c = clusters.getCluster(clusterName);
        MaintenanceState newState = MaintenanceState.valueOf(request.getMaintenanceState());
        MaintenanceState oldState = host.getMaintenanceState(c.getClusterId());
        if (!newState.equals(oldState)) {
          if (newState.equals(MaintenanceState.IMPLIED_FROM_HOST)
              || newState.equals(MaintenanceState.IMPLIED_FROM_SERVICE)) {
            throw new IllegalArgumentException(
                "Invalid arguments, can only set "
                    + "maintenance state to one of "
                    + EnumSet.of(MaintenanceState.OFF, MaintenanceState.ON));
          } else {
            host.setMaintenanceState(c.getClusterId(), newState);
          }
        }
      }

      // Create configurations
      if (null != clusterName && null != request.getDesiredConfigs()) {
        Cluster c = clusters.getCluster(clusterName);

        if (clusters.getHostsForCluster(clusterName).containsKey(host.getHostName())) {

          for (ConfigurationRequest cr : request.getDesiredConfigs()) {

            if (null != cr.getProperties() && cr.getProperties().size() > 0) {
              LOG.info(
                  MessageFormat.format(
                      "Applying configuration with tag ''{0}'' to host ''{1}'' in cluster ''{2}''",
                      cr.getVersionTag(), request.getHostname(), clusterName));

              cr.setClusterName(c.getClusterName());
              controller.createConfiguration(cr);
            }

            Config baseConfig = c.getConfig(cr.getType(), cr.getVersionTag());
            if (null != baseConfig) {
              String authName = controller.getAuthName();
              DesiredConfig oldConfig = host.getDesiredConfigs(c.getClusterId()).get(cr.getType());

              if (host.addDesiredConfig(c.getClusterId(), cr.isSelected(), authName, baseConfig)) {
                Logger logger = LoggerFactory.getLogger("configchange");
                logger.info(
                    "cluster '"
                        + c.getClusterName()
                        + "', "
                        + "host '"
                        + host.getHostName()
                        + "' "
                        + "changed by: '"
                        + authName
                        + "'; "
                        + "type='"
                        + baseConfig.getType()
                        + "' "
                        + "version='"
                        + baseConfig.getVersion()
                        + "'"
                        + "tag='"
                        + baseConfig.getTag()
                        + "'"
                        + (null == oldConfig ? "" : ", from='" + oldConfig.getTag() + "'"));
              }
            }
          }
        }
      }

      if (clusterName != null && !clusterName.isEmpty()) {
        clusters.getCluster(clusterName).recalculateAllClusterVersionStates();
        if (rackChange) {
          controller.registerRackChange(clusterName);
        }
      }

      // todo: if attempt was made to update a property other than those
      // todo: that are allowed above, should throw exception
    }
  }
  /**
   * Accepts a request with registered hosts and if the request contains a cluster name then will
   * map all of the hosts onto that cluster.
   *
   * @param request Request that must contain registered hosts, and optionally a cluster.
   * @throws AmbariException
   */
  public synchronized void createHosts(Request request) throws AmbariException {

    Set<Map<String, Object>> propertySet = request.getProperties();
    if (propertySet == null || propertySet.isEmpty()) {
      LOG.warn("Received a create host request with no associated property sets");
      return;
    }

    AmbariManagementController controller = getManagementController();
    Clusters clusters = controller.getClusters();

    Set<String> duplicates = new HashSet<String>();
    Set<String> unknowns = new HashSet<String>();
    Set<String> allHosts = new HashSet<String>();

    Set<HostRequest> hostRequests = new HashSet<HostRequest>();
    for (Map<String, Object> propertyMap : propertySet) {
      HostRequest hostRequest = getRequest(propertyMap);
      hostRequests.add(hostRequest);
      if (!propertyMap.containsKey(HOSTGROUP_PROPERTY_ID)) {
        createHostResource(clusters, duplicates, unknowns, allHosts, hostRequest);
      }
    }

    if (!duplicates.isEmpty()) {
      StringBuilder names = new StringBuilder();
      boolean first = true;
      for (String hName : duplicates) {
        if (!first) {
          names.append(",");
        }
        first = false;
        names.append(hName);
      }
      throw new IllegalArgumentException(
          "Invalid request contains" + " duplicate hostnames" + ", hostnames=" + names.toString());
    }

    if (!unknowns.isEmpty()) {
      StringBuilder names = new StringBuilder();
      boolean first = true;
      for (String hName : unknowns) {
        if (!first) {
          names.append(",");
        }
        first = false;
        names.append(hName);
      }

      throw new IllegalArgumentException(
          "Attempted to add unknown hosts to a cluster.  "
              + "These hosts have not been registered with the server: "
              + names.toString());
    }

    Map<String, Set<String>> hostClustersMap = new HashMap<String, Set<String>>();
    Map<String, Map<String, String>> hostAttributes = new HashMap<String, Map<String, String>>();
    Set<String> allClusterSet = new HashSet<String>();

    for (HostRequest hostRequest : hostRequests) {
      if (hostRequest.getHostname() != null
          && !hostRequest.getHostname().isEmpty()
          && hostRequest.getClusterName() != null
          && !hostRequest.getClusterName().isEmpty()) {

        Set<String> clusterSet = new HashSet<String>();
        clusterSet.add(hostRequest.getClusterName());
        allClusterSet.add(hostRequest.getClusterName());
        hostClustersMap.put(hostRequest.getHostname(), clusterSet);
        if (hostRequest.getHostAttributes() != null) {
          hostAttributes.put(hostRequest.getHostname(), hostRequest.getHostAttributes());
        }
      }
    }
    clusters.updateHostWithClusterAndAttributes(hostClustersMap, hostAttributes);

    for (String clusterName : allClusterSet) {
      clusters.getCluster(clusterName).recalculateAllClusterVersionStates();
    }
  }