allow scheduling topics to multiple drivers

nova/scheduler/multi.py

@@ -0,0 +1,73 @@
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+# Copyright (c) 2010 Openstack, LLC.
+# Copyright 2010 United States Government as represented by the
+# Administrator of the National Aeronautics and Space Administration.
+# 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.
+
+"""
+Scheduler that allows routing some calls to one driver and others to another.
+"""
+
+from nova import flags
+from nova import utils
+from nova.scheduler import driver
+
+
+FLAGS = flags.FLAGS
+flags.DEFINE_string('compute_scheduler_driver',
+                    'nova.scheduler.chance.ChanceScheduler',
+                    'Driver to use for scheduling compute calls')
+flags.DEFINE_string('volume_scheduler_driver',
+                    'nova.scheduler.chance.ChanceScheduler',
+                    'Driver to use for scheduling volume calls')
+
+
+# A mapping of methods to topics so we can figure out which driver to use.
+_METHOD_MAP = {'run_instance': 'compute',
+               'start_instance': 'compute',
+               'create_volume': 'volume'}
+
+
+class MultiScheduler(driver.Scheduler):
+    """A scheduler that holds multiple sub-schedulers.
+
+    This exists to allow flag-driven composibility of schedulers, allowing
+    third parties to integrate custom schedulers more easily.
+
+    """
+
+    def __init__(self):
+        super(MultiScheduler, self).__init__()
+        compute_driver = utils.import_object(FLAGS.compute_scheduler_driver)
+        volume_driver = utils.import_object(FLAGS.volume_scheduler_driver)
+
+        self.drivers = {'compute': compute_driver,
+                        'volume': volume_driver}
+
+    def __getattr__(self, key):
+        if not key.startswith('schedule_'):
+            raise AttributeError(key)
+        method = key[len('schedule_'):]
+        if method not in _METHOD_MAP:
+            raise AttributeError(key)
+        return getattr(self.drivers[_METHOD_MAP[method]], key)
+
+    def set_zone_manager(self, zone_manager):
+        for k, v in self.drivers.iteritems():
+            v.set_zone_manager(zone_manager)
+
+    def schedule(self, context, topic, *_args, **_kwargs):
+        return self.drivers[topic].schedule(context, topic, *_args, **_kwargs)