diff --git a/watcher/decision_engine/model/element/instance.py b/watcher/decision_engine/model/element/instance.py
index 451998356..ebdb16d7b 100644
--- a/watcher/decision_engine/model/element/instance.py
+++ b/watcher/decision_engine/model/element/instance.py
@@ -48,7 +48,7 @@ class Instance(compute_resource.ComputeResource):
         "disk": wfields.IntegerField(),
         "disk_capacity": wfields.NonNegativeIntegerField(),
         "vcpus": wfields.NonNegativeIntegerField(),
-        "metadata": wfields.DictField(),
+        "metadata": wfields.JsonField(),
     }
 
     def accept(self, visitor):
diff --git a/watcher/decision_engine/model/model_root.py b/watcher/decision_engine/model/model_root.py
index c1843bb90..4daeff5ee 100644
--- a/watcher/decision_engine/model/model_root.py
+++ b/watcher/decision_engine/model/model_root.py
@@ -235,3 +235,10 @@ class ModelRoot(nx.DiGraph, base.Model):
                 model.add_instance(instance)
 
         return model
+
+    @classmethod
+    def is_isomorphic(cls, G1, G2):
+        def node_match(node1, node2):
+            return node1.as_dict() == node2.as_dict()
+        return nx.algorithms.isomorphism.isomorph.is_isomorphic(
+            G1, G2, node_match=node_match)
diff --git a/watcher/decision_engine/strategy/strategies/base.py b/watcher/decision_engine/strategy/strategies/base.py
index 13c241032..effea1e5f 100644
--- a/watcher/decision_engine/strategy/strategies/base.py
+++ b/watcher/decision_engine/strategy/strategies/base.py
@@ -39,6 +39,8 @@ which are dynamically loaded by Watcher at launch time.
 import abc
 import six
 
+from oslo_utils import strutils
+
 from watcher.common import clients
 from watcher.common import context
 from watcher.common import exception
@@ -264,6 +266,22 @@ class BaseStrategy(loadable.Loadable):
     def state_collector(self, s):
         self._cluster_state_collector = s
 
+    def filter_instances_by_audit_tag(self, instances):
+        if not self.config.check_optimize_metadata:
+            return instances
+        instances_to_migrate = []
+        for instance in instances:
+            optimize = True
+            if instance.metadata:
+                try:
+                    optimize = strutils.bool_from_string(
+                        instance.metadata.get('optimize'))
+                except ValueError:
+                    optimize = False
+            if optimize:
+                instances_to_migrate.append(instance)
+        return instances_to_migrate
+
 
 @six.add_metaclass(abc.ABCMeta)
 class DummyBaseStrategy(BaseStrategy):
diff --git a/watcher/decision_engine/strategy/strategies/basic_consolidation.py b/watcher/decision_engine/strategy/strategies/basic_consolidation.py
index 2bb776510..6d9067ff6 100644
--- a/watcher/decision_engine/strategy/strategies/basic_consolidation.py
+++ b/watcher/decision_engine/strategy/strategies/basic_consolidation.py
@@ -159,7 +159,12 @@ class BasicConsolidation(base.ServerConsolidationBaseStrategy):
                 "datasource",
                 help="Data source to use in order to query the needed metrics",
                 default="ceilometer",
-                choices=["ceilometer", "monasca", "gnocchi"])
+                choices=["ceilometer", "monasca", "gnocchi"]),
+            cfg.BoolOpt(
+                "check_optimize_metadata",
+                help="Check optimize metadata field in instance before "
+                     "migration",
+                default=False),
         ]
 
     @property
@@ -437,9 +442,10 @@ class BasicConsolidation(base.ServerConsolidationBaseStrategy):
     def node_and_instance_score(self, sorted_scores):
         """Get List of VMs from node"""
         node_to_release = sorted_scores[len(sorted_scores) - 1][0]
-        instances_to_migrate = self.compute_model.get_node_instances(
+        instances = self.compute_model.get_node_instances(
             self.compute_model.get_node_by_uuid(node_to_release))
 
+        instances_to_migrate = self.filter_instances_by_audit_tag(instances)
         instance_score = []
         for instance in instances_to_migrate:
             if instance.state == element.InstanceState.ACTIVE.value:
diff --git a/watcher/objects/fields.py b/watcher/objects/fields.py
index e05c7b870..d0df8548a 100644
--- a/watcher/objects/fields.py
+++ b/watcher/objects/fields.py
@@ -17,6 +17,7 @@
 import ast
 import six
 
+from oslo_serialization import jsonutils
 from oslo_versionedobjects import fields
 
 
@@ -96,8 +97,26 @@ class FlexibleListOfDictField(fields.AutoTypedField):
         super(FlexibleListOfDictField, self)._null(obj, attr)
 
 
+class Json(fields.FieldType):
+    def coerce(self, obj, attr, value):
+        if isinstance(value, six.string_types):
+            loaded = jsonutils.loads(value)
+            return loaded
+        return value
+
+    def from_primitive(self, obj, attr, value):
+        return self.coerce(obj, attr, value)
+
+    def to_primitive(self, obj, attr, value):
+        return jsonutils.dumps(value)
+
+
+class JsonField(fields.AutoTypedField):
+    AUTO_TYPE = Json()
+
 # ### Notification fields ### #
 
+
 class BaseWatcherEnum(Enum):
 
     ALL = ()
diff --git a/watcher/tests/decision_engine/model/data/scenario_1.xml b/watcher/tests/decision_engine/model/data/scenario_1.xml
index dcf08626d..7476af277 100644
--- a/watcher/tests/decision_engine/model/data/scenario_1.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_1.xml
@@ -1,47 +1,47 @@
 <ModelRoot>
   <ComputeNode human_id="" uuid="Node_0" status="enabled" state="up" id="0" hostname="hostname_0" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_1" status="enabled" state="up" id="1" hostname="hostname_1" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_2" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_2" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_2" status="enabled" state="up" id="2" hostname="hostname_2" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_5" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_5" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_3" status="enabled" state="up" id="3" hostname="hostname_3" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_6" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_6" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_4" status="enabled" state="up" id="4" hostname="hostname_4" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_7" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_7" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
-  <Instance state="active" human_id="" uuid="INSTANCE_10" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_11" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_12" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_13" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_14" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_15" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_16" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_17" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_18" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_19" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_20" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_21" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_22" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_23" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_24" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_25" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_26" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_27" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_28" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_29" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_30" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_31" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_32" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_33" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_34" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_8" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-  <Instance state="active" human_id="" uuid="INSTANCE_9" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+  <Instance state="active" human_id="" uuid="INSTANCE_10" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_11" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_12" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_13" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_14" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_15" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_16" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_17" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_18" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_19" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_20" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_21" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_22" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_23" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_24" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_25" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_26" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_27" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_28" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_29" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_30" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_31" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_32" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_33" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_34" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_8" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+  <Instance state="active" human_id="" uuid="INSTANCE_9" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_1_with_metrics.xml b/watcher/tests/decision_engine/model/data/scenario_1_with_metrics.xml
index 3edf6d17e..d8b80afca 100644
--- a/watcher/tests/decision_engine/model/data/scenario_1_with_metrics.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_1_with_metrics.xml
@@ -1,8 +1,8 @@
 <ModelRoot>
   <ComputeNode hostname="hostname_0" uuid="Node_0" id="0" state="enabled" human_id="" status="enabled" vcpus="40" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_1" uuid="Node_1" id="1" state="enabled" human_id="" status="enabled" vcpus="40" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_2_with_metrics.xml b/watcher/tests/decision_engine/model/data/scenario_2_with_metrics.xml
index 6edba3e7d..668ef1985 100644
--- a/watcher/tests/decision_engine/model/data/scenario_2_with_metrics.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_2_with_metrics.xml
@@ -1,11 +1,11 @@
 <ModelRoot>
   <ComputeNode hostname="hostname_0" uuid="Node_0" id="0" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_1" uuid="Node_1" id="1" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64"/>
   <ComputeNode hostname="hostname_2" uuid="Node_2" id="2" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64"/>
diff --git a/watcher/tests/decision_engine/model/data/scenario_3_with_2_nodes.xml b/watcher/tests/decision_engine/model/data/scenario_3_with_2_nodes.xml
index fee3a27eb..189d81ee9 100644
--- a/watcher/tests/decision_engine/model/data/scenario_3_with_2_nodes.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_3_with_2_nodes.xml
@@ -1,8 +1,8 @@
 <ModelRoot>
   <ComputeNode human_id="" uuid="Node_0" status="enabled" state="up" id="0" hostname="hostname_0" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_1" status="enabled" state="up" id="1" hostname="hostname_1" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="a4cab39b-9828-413a-bf88-f76921bf1517" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="a4cab39b-9828-413a-bf88-f76921bf1517" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_3_with_metrics.xml b/watcher/tests/decision_engine/model/data/scenario_3_with_metrics.xml
index b8987ffd5..5c6079916 100644
--- a/watcher/tests/decision_engine/model/data/scenario_3_with_metrics.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_3_with_metrics.xml
@@ -1,9 +1,9 @@
 <ModelRoot>
   <ComputeNode hostname="hostname_0" uuid="Node_0" id="0" state="up" human_id="" status="enabled" vcpus="10" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_6" vcpus="1" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_7" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_8" vcpus="4" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_9" vcpus="8" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_6" vcpus="1" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_7" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_8" vcpus="4" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_9" vcpus="8" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_1" uuid="Node_1" id="1" state="up" human_id="" status="enabled" vcpus="10" disk="250" disk_capacity="250" memory="64"/>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_5_with_instance_disk_0.xml b/watcher/tests/decision_engine/model/data/scenario_5_with_instance_disk_0.xml
index 72caedbbb..a8bffab30 100644
--- a/watcher/tests/decision_engine/model/data/scenario_5_with_instance_disk_0.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_5_with_instance_disk_0.xml
@@ -1,5 +1,5 @@
 <ModelRoot>
   <ComputeNode human_id="" uuid="Node_0" status="enabled" state="up" id="0" hostname="hostname_0" vcpus="4" disk="4" disk_capacity="4" memory="4">
-    <Instance state="active" human_id="" uuid="INSTANCE_0" vcpus="4" disk="0" disk_capacity="0" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_0" vcpus="4" disk="0" disk_capacity="0" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_6_with_2_nodes.xml b/watcher/tests/decision_engine/model/data/scenario_6_with_2_nodes.xml
index 1ddcf7cab..c12eabaa5 100644
--- a/watcher/tests/decision_engine/model/data/scenario_6_with_2_nodes.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_6_with_2_nodes.xml
@@ -1,10 +1,10 @@
 <ModelRoot>
   <ComputeNode human_id="" uuid="Node_0" status="enabled" state="up" id="0" hostname="hostname_0" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_1" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_1" status="enabled" state="up" id="1" hostname="hostname_1" vcpus="40" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_7_with_2_nodes.xml b/watcher/tests/decision_engine/model/data/scenario_7_with_2_nodes.xml
index 1da834336..99ee529a8 100644
--- a/watcher/tests/decision_engine/model/data/scenario_7_with_2_nodes.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_7_with_2_nodes.xml
@@ -1,10 +1,10 @@
 <ModelRoot>
   <ComputeNode human_id="" uuid="Node_0" status="enabled" state="up" id="0" hostname="hostname_0" vcpus="50" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="cae81432-1631-4d4e-b29c-6f3acdcde906" vcpus="15" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="73b09e16-35b7-4922-804e-e8f5d9b740fc" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="cae81432-1631-4d4e-b29c-6f3acdcde906" vcpus="15" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode human_id="" uuid="Node_1" status="enabled" state="up" id="1" hostname="hostname_1" vcpus="50" disk="250" disk_capacity="250" memory="132">
-    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
-    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2"/>
+    <Instance state="active" human_id="" uuid="INSTANCE_3" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance state="active" human_id="" uuid="INSTANCE_4" vcpus="10" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_8_with_4_nodes.xml b/watcher/tests/decision_engine/model/data/scenario_8_with_4_nodes.xml
index 6e619c4a7..a646c6e90 100644
--- a/watcher/tests/decision_engine/model/data/scenario_8_with_4_nodes.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_8_with_4_nodes.xml
@@ -1,16 +1,16 @@
 <ModelRoot>
   <ComputeNode hostname="hostname_0" uuid="Node_0" id="0" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_1" uuid="Node_1" id="1" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_2" uuid="Node_2" id="2" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_3" uuid="Node_3" id="3" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/data/scenario_9_with_3_active_plus_1_disabled_nodes.xml b/watcher/tests/decision_engine/model/data/scenario_9_with_3_active_plus_1_disabled_nodes.xml
index 33396d824..d1d3f94eb 100644
--- a/watcher/tests/decision_engine/model/data/scenario_9_with_3_active_plus_1_disabled_nodes.xml
+++ b/watcher/tests/decision_engine/model/data/scenario_9_with_3_active_plus_1_disabled_nodes.xml
@@ -1,16 +1,16 @@
 <ModelRoot>
   <ComputeNode hostname="hostname_0" uuid="Node_0" id="0" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
-    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_0" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_1" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
+    <Instance human_id="" state="active" uuid="INSTANCE_2" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_1" uuid="Node_1" id="1" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_3" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_2" uuid="Node_2" id="2" state="up" human_id="" status="enabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_4" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
   <ComputeNode hostname="hostname_3" uuid="Node_3" id="3" state="up" human_id="" status="disabled" vcpus="16" disk="250" disk_capacity="250" memory="64">
-    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="2" disk="20" disk_capacity="20" memory="2"/>
+    <Instance human_id="" state="active" uuid="INSTANCE_5" vcpus="2" disk="20" disk_capacity="20" memory="2" metadata='{"optimize": true,"top": "floor", "nested": {"x": "y"}}'/>
   </ComputeNode>
 </ModelRoot>
diff --git a/watcher/tests/decision_engine/model/faker_cluster_state.py b/watcher/tests/decision_engine/model/faker_cluster_state.py
index 66dd5e1cd..2be8222ec 100644
--- a/watcher/tests/decision_engine/model/faker_cluster_state.py
+++ b/watcher/tests/decision_engine/model/faker_cluster_state.py
@@ -85,6 +85,8 @@ class FakerModelCollector(base.BaseClusterDataModelCollector):
                 "disk": 20,
                 "disk_capacity": 20,
                 "vcpus": 10,
+                "metadata":
+                    '{"optimize": true,"top": "floor","nested": {"x": "y"}}'
             }
 
             instance = element.Instance(**instance_attributes)
diff --git a/watcher/tests/decision_engine/model/test_model.py b/watcher/tests/decision_engine/model/test_model.py
index 65c364afe..d8438dc43 100644
--- a/watcher/tests/decision_engine/model/test_model.py
+++ b/watcher/tests/decision_engine/model/test_model.py
@@ -18,9 +18,7 @@
 
 import os
 
-from lxml import etree
 from oslo_utils import uuidutils
-import six
 
 from watcher.common import exception
 from watcher.decision_engine.model import element
@@ -45,26 +43,16 @@ class TestModel(base.TestCase):
 
     def test_model_structure(self):
         fake_cluster = faker_cluster_state.FakerModelCollector()
-        model = fake_cluster.build_scenario_1()
+        model1 = fake_cluster.build_scenario_1()
 
-        self.assertEqual(5, len(model.get_all_compute_nodes()))
-        self.assertEqual(35, len(model.get_all_instances()))
-        self.assertEqual(8, len(model.edges()))
+        self.assertEqual(5, len(model1.get_all_compute_nodes()))
+        self.assertEqual(35, len(model1.get_all_instances()))
+        self.assertEqual(8, len(model1.edges()))
 
         expected_struct_str = self.load_data('scenario_1.xml')
-        parser = etree.XMLParser(remove_blank_text=True)
-        expected_struct = etree.fromstring(expected_struct_str, parser)
-        model_structure = etree.fromstring(model.to_string(), parser)
+        model2 = model_root.ModelRoot.from_xml(expected_struct_str)
 
-        normalized_expected_output = six.BytesIO()
-        normalized_model_output = six.BytesIO()
-        expected_struct.getroottree().write_c14n(normalized_expected_output)
-        model_structure.getroottree().write_c14n(normalized_model_output)
-
-        normalized_expected_struct = normalized_expected_output.getvalue()
-        normalized_model_struct = normalized_model_output.getvalue()
-
-        self.assertEqual(normalized_expected_struct, normalized_model_struct)
+        self.assertTrue(model_root.ModelRoot.is_isomorphic(model2, model1))
 
     def test_build_model_from_xml(self):
         fake_cluster = faker_cluster_state.FakerModelCollector()