text: # Copyright (c) 2011-2012 OpenStack Foundation.
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  from essential.scheduler import filters
  
  
  class AvailabilityZoneFilter(filters.BaseHostFilter):
      """Filters Hosts by availability zone."""
  
      # Availability zones do not change within a request
      run_filter_once_per_request = True
  
      def host_passes(self, host_state, filter_properties):
          spec = filter_properties.get('request_spec', {})
          props = spec.get('resource_properties', {})
          availability_zone = props.get('availability_zone')
  
          if availability_zone:
              return availability_zone == host_state.service['availability_zone']
          return True
  