First cut with tests passing

nova/scheduler/api.py

@@ -81,6 +81,12 @@ def get_zone_capabilities(context):
     return _call_scheduler('get_zone_capabilities', context=context)
 
 
+def select(context, specs=None):
+    """Returns a list of hosts."""
+    return _call_scheduler('select', context=context,
+            params={"specs": specs})
+
+
 def update_service_capabilities(context, service_name, host, capabilities):
     """Send an update to all the scheduler services informing them
        of the capabilities of this service."""

nova/scheduler/zone_aware_scheduler.py

@@ -0,0 +1,88 @@
+# Copyright (c) 2011 Openstack, LLC.
+# 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.
+
+"""
+The Zone Aware Scheduler is a base class Scheduler for creating instances
+across zones. There are two expansion points to this class for:
+1. Assigning Weights to hosts for requested instances
+2. Filtering Hosts based on required instance capabilities
+"""
+
+import operator
+
+from nova import log as logging
+from nova.scheduler import api
+
+LOG = logging.getLogger('nova.scheduler.zone_aware_scheduler')
+
+
+class ZoneAwareScheduler(object):
+    """Base class for creating Zone Aware Schedulers."""
+
+    def _call_zone_method(self, context, method, specs):
+        """Call novaclient zone method. Broken out for testing."""
+        return api.call_zone_method(context, method, specs=specs)
+
+    def select(self, context, *args, **kwargs):
+        """Select returns a list of weights and zone/host information
+        corresponding to the best hosts to service the request. Any
+        child zone information has been encrypted so as not to reveal
+        anything about the children."""
+        return self._schedule(context, "compute", *args, **kwargs)
+
+   def schedule(self, context, topic, *args, **kwargs):
+        """The schedule() contract requires we return the one
+        best-suited host for this request.
+        """
+        res = self._schedule(context, topic, *args, **kwargs)
+        return res[0]
+
+    def _schedule(self, context, topic, *args, **kwargs):
+        """Returns a list of hosts that meet the required specs,
+        ordered by their fitness.
+        """
+        # Filter local hosts based on requirements ...
+        host_list = self.filter_hosts()
+
+        # then weigh the selected hosts.
+        # weighted = [ { 'weight':#, 'name':host, ...}, ]
+        weighted = self.weight_hosts(host_list)
+
+        # Next, tack on the best weights from the child zones ...
+        child_results = self._call_zone_method(context, "select",
+                specs=specs)
+        for child_zone, result in child_results:
+            for weighting in result:
+                # Remember the child_zone so we can get back to
+                # it later if needed. This implicitly builds a zone
+                # path structure.
+                host_dict = {
+                        "weight": weighting["weight"],
+                        "child_zone": child_zone,
+                        "child_blob": weighting["blob"]}
+                weighted.append(host_dict)
+
+        weighted.sort(key=operator.itemgetter('weight'))
+        return weighted
+
+   def filter_hosts(self):
+       """Derived classes must override this method and return
+          a list of hosts in [?] format."""
+          raise NotImplemented()
+
+   def weigh_hosts(self, hosts):
+       """Derived classes must override this method and return
+          a lists of hosts in [?] format."""
+          raise NotImplemented()