Retry attachment delete API call for 504 Gateway Timeout

When cinder-api runs behind a load balancer(eg haproxy), the load
balancer can return 504 Gateway Timeout when cinder-api does not
respond within timeout. This change ensures nova retries deleting
a volume attachment in that case.

Also this change makes nova ignore 404 in the API call. This is
required because cinder might continue deleting the attachment even if
the load balancer returns 504. This also helps us in the situation
where the volume attachment was accidentally removed by users.

Closes-Bug: #1978444
Change-Id: I593011d9f4c43cdae7a3d53b556c6e2a2b939989

3 files changed, 54 insertions, 11 deletions

diff --git a/nova/tests/unit/volume/test_cinder.py b/nova/tests/unit/volume/test_cinder.py
index 0c170c05e4..f4ee7383d4 100644
--- a/nova/tests/unit/volume/test_cinder.py
+++ b/nova/tests/unit/volume/test_cinder.py
@@ -520,16 +520,15 @@ class CinderApiTestCase(test.NoDBTestCase):
     @mock.patch('nova.volume.cinder.cinderclient')
     def test_attachment_delete_failed(self, mock_cinderclient, mock_log):
         mock_cinderclient.return_value.attachments.delete.side_effect = (
-                cinder_exception.NotFound(404, '404'))
+                cinder_exception.BadRequest(400, '400'))
 
         attachment_id = uuids.attachment
-        ex = self.assertRaises(exception.VolumeAttachmentNotFound,
+        ex = self.assertRaises(exception.InvalidInput,
                                self.api.attachment_delete,
                                self.ctx,
                                attachment_id)
 
-        self.assertEqual(404, ex.code)
-        self.assertIn(attachment_id, str(ex))
+        self.assertEqual(400, ex.code)
 
     @mock.patch('nova.volume.cinder.cinderclient',
                 side_effect=exception.CinderAPIVersionNotAvailable(
@@ -546,6 +545,16 @@ class CinderApiTestCase(test.NoDBTestCase):
                                                   skip_version_check=True)
 
     @mock.patch('nova.volume.cinder.cinderclient')
+    def test_attachment_delete_not_found(self, mock_cinderclient):
+        mock_cinderclient.return_value.attachments.delete.side_effect = (
+            cinder_exception.ClientException(404))
+
+        attachment_id = uuids.attachment
+        self.api.attachment_delete(self.ctx, attachment_id)
+
+        self.assertEqual(1, mock_cinderclient.call_count)
+
+    @mock.patch('nova.volume.cinder.cinderclient')
     def test_attachment_delete_internal_server_error(self, mock_cinderclient):
         mock_cinderclient.return_value.attachments.delete.side_effect = (
             cinder_exception.ClientException(500))
@@ -569,6 +578,29 @@ class CinderApiTestCase(test.NoDBTestCase):
         self.assertEqual(2, mock_cinderclient.call_count)
 
     @mock.patch('nova.volume.cinder.cinderclient')
+    def test_attachment_delete_gateway_timeout(self, mock_cinderclient):
+        mock_cinderclient.return_value.attachments.delete.side_effect = (
+            cinder_exception.ClientException(504))
+
+        self.assertRaises(cinder_exception.ClientException,
+                          self.api.attachment_delete,
+                          self.ctx, uuids.attachment_id)
+
+        self.assertEqual(5, mock_cinderclient.call_count)
+
+    @mock.patch('nova.volume.cinder.cinderclient')
+    def test_attachment_delete_gateway_timeout_do_not_raise(
+                                                      self, mock_cinderclient):
+        # generate exception, and then have a normal return on the next retry
+        mock_cinderclient.return_value.attachments.delete.side_effect = [
+            cinder_exception.ClientException(504), None]
+
+        attachment_id = uuids.attachment
+        self.api.attachment_delete(self.ctx, attachment_id)
+
+        self.assertEqual(2, mock_cinderclient.call_count)
+
+    @mock.patch('nova.volume.cinder.cinderclient')
     def test_attachment_delete_bad_request_exception(self, mock_cinderclient):
         mock_cinderclient.return_value.attachments.delete.side_effect = (
             cinder_exception.BadRequest(400))
diff --git a/nova/volume/cinder.py b/nova/volume/cinder.py
index bf1e455bba..01efcfec19 100644
--- a/nova/volume/cinder.py
+++ b/nova/volume/cinder.py
@@ -888,19 +888,23 @@ class API(object):
     @retrying.retry(stop_max_attempt_number=5,
                     retry_on_exception=lambda e:
                     (isinstance(e, cinder_exception.ClientException) and
-                     e.code == 500))
+                     e.code in (500, 504)))
     def attachment_delete(self, context, attachment_id):
         try:
             cinderclient(
                 context, '3.44', skip_version_check=True).attachments.delete(
                     attachment_id)
         except cinder_exception.ClientException as ex:
-            with excutils.save_and_reraise_exception():
-                LOG.error('Delete attachment failed for attachment '
-                          '%(id)s. Error: %(msg)s Code: %(code)s',
-                          {'id': attachment_id,
-                           'msg': str(ex),
-                           'code': getattr(ex, 'code', None)})
+            if ex.code == 404:
+                LOG.warning('Attachment %(id)s does not exist. Ignoring.',
+                            {'id': attachment_id})
+            else:
+                with excutils.save_and_reraise_exception():
+                    LOG.error('Delete attachment failed for attachment '
+                              '%(id)s. Error: %(msg)s Code: %(code)s',
+                              {'id': attachment_id,
+                               'msg': str(ex),
+                               'code': getattr(ex, 'code', None)})
 
     @translate_attachment_exception
     def attachment_complete(self, context, attachment_id):
diff --git a/releasenotes/notes/bug-1978444-db46df5f3d5ea19e.yaml b/releasenotes/notes/bug-1978444-db46df5f3d5ea19e.yaml
new file mode 100644
index 0000000000..6c19804074
--- /dev/null
+++ b/releasenotes/notes/bug-1978444-db46df5f3d5ea19e.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    `Bug #1978444 <https://bugs.launchpad.net/nova/+bug/1978444>`_: Now nova
+    retries deleting a volume attachment in case Cinder API returns
+    ``504 Gateway Timeout``. Also, ``404 Not Found`` is now ignored and
+    leaves only a warning message.