Optimized describing of instance.

Change-Id: I4685621ce72ef4004fc05b2628493b8c5b8f0fd5

ec2api/api/common.py

@@ -332,14 +332,11 @@ class UniversalDescriber(object):
 
     def describe(self, context, ids=None, names=None, filter=None):
         self.context = context
-        selective_describe = ids is not None or names is not None
+        self.selective_describe = ids is not None or names is not None
         self.ids = set(ids or [])
         self.names = set(names or [])
-        # NOTE(Alex): OS items are retrieved here first to let specific
-        # describer a chance to recreate some default object and refresh
-        # the db items before their retrieval.
-        self.os_items = self.get_os_items()
         self.items = self.get_db_items()
+        self.os_items = self.get_os_items()
         formatted_items = []
 
         self.items_dict = {i['os_id']: i for i in (self.items or [])}
@@ -349,7 +346,7 @@ class UniversalDescriber(object):
             os_item_id = self.get_id(os_item)
             item = self.items_dict.get(os_item_id, None)
             # NOTE(Alex): Filter out items not requested in names or ids
-            if (selective_describe and
+            if (self.selective_describe and
                     not (os_item_name in self.names or
                          (item and item['id'] in self.ids))):
                 continue

ec2api/api/instance.py

@@ -43,7 +43,7 @@ ec2_opts = [
                      'describe instances'),
     cfg.StrOpt('default_flavor',
            default='m1.small',
-           help='A flavor to use as a default instance type'),
+           help='A flavor to use as a default instance type')
 ]
 
 CONF = cfg.CONF
@@ -323,7 +323,13 @@ class InstanceDescriber(common.TaggableItemsDescriber):
         self.os_volumes = _get_os_volumes(self.context)
         self.os_flavors = _get_os_flavors(self.context)
         nova = clients.nova(ec2_context.get_os_admin_context())
-        return nova.servers.list(
+        if self.ids == 1 and len(self.items) == 1:
+            try:
+                return [nova.servers.get(self.items[0]['os_id'])]
+            except nova_exception.NotFound:
+                return []
+        else:
+            return nova.servers.list(
                 search_opts={'all_tenants': True,
                              'project_id': self.context.project_id})
 

ec2api/api/security_group.py

@@ -140,6 +140,7 @@ class SecurityGroupDescriber(common.TaggableItemsDescriber):
         os_groups = security_group_engine.get_os_groups(self.context)
         if self.check_and_repair_default_groups(os_groups, self.all_db_items):
             self.all_db_items = db_api.get_items(self.context, 'sg')
+            self.items = self.get_db_items()
             os_groups = security_group_engine.get_os_groups(self.context)
         for os_group in os_groups:
             os_group['name'] = _translate_group_name(self.context,

ec2api/tests/unit/test_instance.py

@@ -703,6 +703,8 @@ class InstanceTestCase(base.ApiTestCase):
         self.nova_admin.servers.list.return_value = [
             fakes.OSInstance_full(fakes.OS_INSTANCE_1),
             fakes.OSInstance_full(fakes.OS_INSTANCE_2)]
+        self.nova_admin.servers.get.return_value = (
+            fakes.OSInstance_full(fakes.OS_INSTANCE_1))
         self.cinder.volumes.list.return_value = [
             fakes.OSVolume(fakes.OS_VOLUME_1),
             fakes.OSVolume(fakes.OS_VOLUME_2),