gistfile1.txt

diff --git a/nova/objects/instance.py b/nova/objects/instance.py
index 4ee3ca9..a3974af 100644
--- a/nova/objects/instance.py
+++ b/nova/objects/instance.py
@@ -88,7 +88,8 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
                base.NovaObjectDictCompat):
     # Version 2.0: Initial version
     # Version 2.1: Added services
-    VERSION = '2.1'
+    # version 2.2: add foo
+    VERSION = '2.2'
 
     fields = {
         'id': fields.IntegerField(),
@@ -186,7 +187,8 @@ class Instance(base.NovaPersistentObject, base.NovaObject,
         'vcpu_model': fields.ObjectField('VirtCPUModel', nullable=True),
         'ec2_ids': fields.ObjectField('EC2Ids'),
         'migration_context': fields.ObjectField('MigrationContext',
-                                                nullable=True)
+                                                nullable=True),
+        'foo': fields.StringField(nullable=True),
         }
 
     obj_extra_fields = ['name']