diff --git a/nova/compute/resource_tracker.py b/nova/compute/resource_tracker.py
index 39297a860f94..b1af3ffe5bc3 100644
--- a/nova/compute/resource_tracker.py
+++ b/nova/compute/resource_tracker.py
@@ -616,10 +616,31 @@ class ResourceTracker(object):
         stats.digest_stats(resources.get('stats'))
         compute_node.stats = stats
 
-        # update the allocation ratios for the related ComputeNode object
-        compute_node.ram_allocation_ratio = self.ram_allocation_ratio
-        compute_node.cpu_allocation_ratio = self.cpu_allocation_ratio
-        compute_node.disk_allocation_ratio = self.disk_allocation_ratio
+        # Update the allocation ratios for the related ComputeNode object
+        # but only if the configured values are not the default 0.0; the
+        # ComputeNode._from_db_object method takes care of providing default
+        # allocation ratios when the config is left at the 0.0 default, so
+        # we'll really end up with something like a
+        # ComputeNode.cpu_allocation_ratio of 16.0, not 0.0. We want to avoid
+        # resetting the ComputeNode fields to 0.0 because that will make
+        # the _resource_change method think something changed when really it
+        # didn't.
+        # TODO(mriedem): Will this break any scenarios where an operator is
+        # trying to *reset* the allocation ratios by changing config from
+        # non-0.0 back to 0.0? Maybe we should only do this if the fields on
+        # the ComputeNode object are not already set. For example, let's say
+        # the cpu_allocation_ratio config was 1.0 and then the operator wants
+        # to get back to the default (16.0 via the facade), and to do that they
+        # change the config back to 0.0 (or just unset the config option).
+        # Should we support that or treat these config options as "sticky" in
+        # that once you start setting them, you can't go back to the implied
+        # defaults by unsetting or resetting to 0.0? Sort of like how
+        # per-tenant quota is sticky once you change it in the API.
+        for res in ('cpu', 'disk', 'ram'):
+            attr = '%s_allocation_ratio' % res
+            conf_alloc_ratio = getattr(self, attr)
+            if conf_alloc_ratio != 0.0:
+                setattr(compute_node, attr, conf_alloc_ratio)
 
         # now copy rest to compute_node
         compute_node.update_from_virt_driver(resources)
diff --git a/nova/tests/unit/compute/test_resource_tracker.py b/nova/tests/unit/compute/test_resource_tracker.py
index be6e3be4f0ed..9d5530a078a8 100644
--- a/nova/tests/unit/compute/test_resource_tracker.py
+++ b/nova/tests/unit/compute/test_resource_tracker.py
@@ -1333,6 +1333,41 @@ class TestUpdateComputeNode(BaseTestCase):
         self.assertRaises(exc.ComputeHostNotFound,
                           self.rt.get_node_uuid, 'foo')
 
+    def test_copy_resources_no_update_allocation_ratios(self):
+        """Tests that a ComputeNode object's allocation ratio fields are
+        not set if the configured allocation ratio values are default 0.0.
+        """
+        self._setup_rt()
+        compute = _COMPUTE_NODE_FIXTURES[0].obj_clone()
+        compute.obj_reset_changes()  # make sure we start clean
+        self.rt._copy_resources(
+            compute, self.driver_mock.get_available_resource.return_value)
+        # Assert that the ComputeNode fields were not changed.
+        changes = compute.obj_get_changes()
+        for res in ('cpu', 'disk', 'ram'):
+            attr_name = '%s_allocation_ratio' % res
+            self.assertNotIn(attr_name, changes)
+
+    def test_copy_resources_update_allocation_ratios_from_config(self):
+        """Tests that a ComputeNode object's allocation ratio fields are
+        set if the configured allocation ratio values are not 0.0.
+        """
+        # Set explicit ratio config values to 1.0 (the default is 0.0).
+        for res in ('cpu', 'disk', 'ram'):
+            opt_name = '%s_allocation_ratio' % res
+            CONF.set_override(opt_name, 1.0)
+        self._setup_rt()
+        compute = _COMPUTE_NODE_FIXTURES[0].obj_clone()
+        compute.obj_reset_changes()  # make sure we start clean
+        self.rt._copy_resources(
+            compute, self.driver_mock.get_available_resource.return_value)
+        # Assert that the ComputeNode fields were changed.
+        changes = compute.obj_get_changes()
+        for res in ('cpu', 'disk', 'ram'):
+            attr_name = '%s_allocation_ratio' % res
+            self.assertIn(attr_name, changes)
+            self.assertEqual(1.0, changes[attr_name])
+
 
 class TestNormalizatInventoryFromComputeNode(test.NoDBTestCase):
     def test_normalize_libvirt(self):