Simplify and optimize az server output extension.

Displaying two different az results to users is confusing, so just
return the az that the instance is actually in. Also, cache the
result from looking up the az by host for an hour to avoid making
lots of expensive db requests.

DocImpact

Change-Id: Ib39bf94c608874695aab00e61035e64f9594a985

1 files changed, 16 insertions, 11 deletions

diff --git a/nova/api/openstack/compute/contrib/extended_availability_zone.py b/nova/api/openstack/compute/contrib/extended_availability_zone.py
index b7451cb6a..734ddf7c8 100644
--- a/nova/api/openstack/compute/contrib/extended_availability_zone.py
+++ b/nova/api/openstack/compute/contrib/extended_availability_zone.py
@@ -21,26 +21,35 @@ 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.common import memorycache
 from nova.openstack.common import log as logging
 
 LOG = logging.getLogger(__name__)
+# 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):
-        admin_context = context.elevated()
-        if instance['host']:
-            return availability_zones.get_host_availability_zone(
-                                            admin_context, instance['host'])
+        host = 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] = instance.get('availability_zone', None)
-
-        key = "%s:host_availability_zone" % Extended_availability_zone.alias
         server[key] = self._get_host_az(context, instance)
 
     @wsgi.extends
@@ -81,10 +90,6 @@ class Extended_availability_zone(extensions.ExtensionDescriptor):
 def make_server(elem):
     elem.set('{%s}availability_zone' % Extended_availability_zone.namespace,
              '%s:availability_zone' % Extended_availability_zone.alias)
-    elem.set('{%s}host_availability_zone' %
-             Extended_availability_zone.namespace,
-             '%s:host_availability_zone' %
-             Extended_availability_zone.alias)
 
 
 class ExtendedAZTemplate(xmlutil.TemplateBuilder):