diff --git a/plstackapi/core/models/plcorebase.py b/plstackapi/core/models/plcorebase.py
index 52aa0f7..eac3114 100644
--- a/plstackapi/core/models/plcorebase.py
+++ b/plstackapi/core/models/plcorebase.py
@@ -1,5 +1,6 @@
 import os
 from django.db import models
+from django.forms.models import model_to_dict
 
 class PlCoreBase(models.Model):
 
@@ -10,5 +11,36 @@
         abstract = True
         app_label = "core"
 
+    def __init__(self, *args, **kwargs):
+        super(PlCoreBase, self).__init__(*args, **kwargs)
+        self.__initial = self._dict
+
+    @property
+    def diff(self):
+        d1 = self.__initial
+        d2 = self._dict
+        diffs = [(k, (v, d2[k])) for k, v in d1.items() if v != d2[k]]
+        return dict(diffs)
+
+    @property
+    def has_changed(self):
+        return bool(self.diff)
+
+    @property
+    def changed_fields(self):
+        return self.diff.keys()
+
+    def get_field_diff(self, field_name):
+        return self.diff.get(field_name, None)
+
+    def save(self, *args, **kwargs):
+        super(PlCoreBase, self).save(*args, **kwargs)
+        self.__initial = self._dict
+
+    @property
+    def _dict(self):
+        return model_to_dict(self, fields=[field.name for field in
+                             self._meta.fields])
+
 
 
diff --git a/plstackapi/openstack/manager.py b/plstackapi/openstack/manager.py
index 171946e..f991676 100644
--- a/plstackapi/openstack/manager.py
+++ b/plstackapi/openstack/manager.py
@@ -215,7 +215,7 @@
             sliver.instance_id = instance.id
             sliver.instance_name = getattr(instance, 'OS-EXT-SRV-ATTR:instance_name')
 
-        if sliver.instance_id:
+        if sliver.instance_id and ("numberCores" in sliver.changed_fields):
             self.driver.update_instance_metadata(sliver.instance_id, {"cpu_cores": str(sliver.numberCores)})
 
     @require_enabled