diff --git a/ceilometer/publisher/gnocchi.py b/ceilometer/publisher/gnocchi.py
index cdebfc14f5..558d3a53bd 100644
--- a/ceilometer/publisher/gnocchi.py
+++ b/ceilometer/publisher/gnocchi.py
@@ -411,11 +411,19 @@ class GnocchiPublisher(publisher.ConfigPublisherBase):
                     gnocchi_data[resource_id] = {
                         'resource_type': rd.cfg['resource_type'],
                         'resource': {"id": resource_id,
-                                     "user_id": sample.user_id,
-                                     "project_id": sample.project_id}}
+                                     "user_id": sample.user_id}}
 
+                # NOTE(callumdickinson): project_id is added to resource_extra
+                # because the project that owns the resource can change (e.g.
+                # transferred volumes), and we want this reflected in Gnocchi.
+                # user_id is not treated this way because it is not always
+                # available on all samples for a given metric, and because in
+                # some cases updating it would cause resource updates to occur
+                # every time a new user performs a request against a resource.
                 gnocchi_data[resource_id].setdefault(
-                    "resource_extra", {}).update(rd.sample_attributes(sample))
+                    "resource_extra", {}).update({
+                        "project_id": sample.project_id,
+                        **rd.sample_attributes(sample)})
                 measures.setdefault(resource_id, {}).setdefault(
                     metric_name,
                     {"measures": [],
diff --git a/ceilometer/tests/unit/publisher/test_gnocchi.py b/ceilometer/tests/unit/publisher/test_gnocchi.py
index 5754611800..d4eb2de185 100644
--- a/ceilometer/tests/unit/publisher/test_gnocchi.py
+++ b/ceilometer/tests/unit/publisher/test_gnocchi.py
@@ -872,10 +872,13 @@ class PublisherWorkflowTest(base.BaseTestCase,
                           1, 1)
             )
 
-        if self.patchable_attributes:
+        update_attributes = {**self.postable_attributes,
+                             **self.patchable_attributes}
+        del update_attributes["user_id"]  # Only user_id is not updated.
+        if self.patchable_attributes != update_attributes:
             expected_calls.append(mock.call.resource.update(
                 self.resource_type, resource_id,
-                self.patchable_attributes))
+                update_attributes))
             if self.update_resource_fail:
                 fakeclient.resource.update.side_effect = [Exception('boom!')]
             else:
@@ -891,9 +894,9 @@ class PublisherWorkflowTest(base.BaseTestCase,
         if (self.post_measure_fail
                 or self.create_resource_fail
                 or self.retry_post_measures_fail
-                or (self.update_resource_fail and self.patchable_attributes)):
+                or (self.update_resource_fail and update_attributes)):
 
-            if self.update_resource_fail and self.patchable_attributes:
+            if self.update_resource_fail and update_attributes:
                 logger.error.assert_called_with(
                     'Unexpected exception updating resource type [%s] with '
                     'ID [%s] for resource data [%s]: [%s].', resource_type,
diff --git a/releasenotes/notes/gnocchi-update-project-id-c8355fc5901e7aa3.yaml b/releasenotes/notes/gnocchi-update-project-id-c8355fc5901e7aa3.yaml
new file mode 100644
index 0000000000..6eb1890a49
--- /dev/null
+++ b/releasenotes/notes/gnocchi-update-project-id-c8355fc5901e7aa3.yaml
@@ -0,0 +1,13 @@
+---
+upgrade:
+  - |
+    If resource metadata caching is enabled in Ceilometer Notification Agent,
+    the Gnocchi resource metadata cache will be invalidated and refreshed upon
+    upgrading due to the fix for updating resource project IDs.
+fixes:
+  - |
+    An issue has been fixed where when publishing resource metadata changes to
+    Gnocchi, the project ID field was not updated when changed (e.g. when
+    transferring volumes from one project to another). Any existing resources
+    that have changed ownership since being added to Gnocchi will have their
+    ``project_id`` attribute updated to the correct value.