Extract getting instance's AZ into a helper module.

An instance's availability zone logic may used by many modules,
so move it from extend API into helper module `nova.availability_zones`.
Also add some tests for the new method.

part of bp: different-availability-zone-filter

Change-Id: I5916a0b09d5dddec338e8e36503953720dfd6bcd

nova/api/openstack/compute/contrib/extended_availability_zone.py

@@ -21,34 +21,16 @@ from nova.api.openstack import extensions
 from nova.api.openstack import wsgi
 from nova.api.openstack import xmlutil
 from nova import availability_zones
-from nova.openstack.common import memorycache
 
-# NOTE(vish): azs don't change that often, so cache them for an hour to
-#             avoid hitting the db multiple times on every request.
-AZ_CACHE_SECONDS = 60 * 60
 authorize = extensions.soft_extension_authorizer('compute',
                                                  'extended_availability_zone')
 
 
 class ExtendedAZController(wsgi.Controller):
-    def __init__(self):
-        self.mc = memorycache.get_client()
-
-    def _get_host_az(self, context, instance):
-        host = str(instance.get('host'))
-        if not host:
-            return None
-        cache_key = "azcache-%s" % host
-        az = self.mc.get(cache_key)
-        if not az:
-            elevated = context.elevated()
-            az = availability_zones.get_host_availability_zone(elevated, host)
-            self.mc.set(cache_key, az, AZ_CACHE_SECONDS)
-        return az
-
     def _extend_server(self, context, server, instance):
         key = "%s:availability_zone" % Extended_availability_zone.alias
-        server[key] = self._get_host_az(context, instance)
+        server[key] = availability_zones.get_instance_availability_zone(
+                                                            context, instance)
 
     @wsgi.extends
     def show(self, req, resp_obj, id):

nova/availability_zones.py

@@ -18,6 +18,12 @@
 from oslo.config import cfg
 
 from nova import db
+from nova.openstack.common import memorycache
+
+# NOTE(vish): azs don't change that often, so cache them for an hour to
+#             avoid hitting the db multiple times on every request.
+AZ_CACHE_SECONDS = 60 * 60
+MC = memorycache.get_client()
 
 availability_zone_opts = [
     cfg.StrOpt('internal_service_availability_zone',
@@ -81,3 +87,18 @@ def get_availability_zones(context):
         if zone not in not_available_zones:
             not_available_zones.append(zone)
     return (available_zones, not_available_zones)
+
+
+def get_instance_availability_zone(context, instance):
+    """Return availability zone of specified instance."""
+    host = str(instance.get('host'))
+    if not host:
+        return None
+
+    cache_key = "azcache-%s" % host
+    az = MC.get(cache_key)
+    if not az:
+        elevated = context.elevated()
+        az = get_host_availability_zone(elevated, host)
+        MC.set(cache_key, az, AZ_CACHE_SECONDS)
+    return az

nova/tests/test_availability_zones.py

@@ -25,6 +25,7 @@ from nova import availability_zones as az
 from nova import context
 from nova import db
 from nova import test
+from nova.tests.api.openstack import fakes
 
 CONF = cfg.CONF
 CONF.import_opt('internal_service_availability_zone',
@@ -155,3 +156,23 @@ class AvailabilityZoneTestCases(test.TestCase):
 
         self.assertEquals(zones, ['nova-test', 'nova-test2'])
         self.assertEquals(not_zones, ['nova-test3', 'nova'])
+
+    def test_get_instance_availability_zone_default_value(self):
+        """Test get right availability zone by given an instance."""
+        fake_inst_id = 162
+        fake_inst = fakes.stub_instance(fake_inst_id, host=self.host)
+
+        self.assertEqual(self.default_az,
+                az.get_instance_availability_zone(self.context, fake_inst))
+
+    def test_get_instance_availability_zone_from_aggregate(self):
+        """Test get availability zone from aggregate by given an instance."""
+        host = 'host170'
+        service = self._create_service_with_topic('compute', host)
+        self._add_to_aggregate(service, self.agg)
+
+        fake_inst_id = 174
+        fake_inst = fakes.stub_instance(fake_inst_id, host=host)
+
+        self.assertEqual(self.availability_zone,
+                az.get_instance_availability_zone(self.context, fake_inst))