Make archive_deleted_rows handle a missing CONF.api_database.connection

This change https://review.openstack.org/#/c/515034/ (added in queens)
makes the archive_deleted_rows CLI remove instance mappings and request
specs from the API database if there are instances archived from the
main nova/cell database. However for this to work, the api database
connection should be set in the config file. So in the case that the
API database is not configured in the config file being used to run the
CLI, we should gracefully handle the condition and and stop archiving thus
prompting the user to set the api_db config and try the archival operation
again. This patch fixes the graceful handling.

Conflicts:
    nova/tests/unit/test_nova_manage.py

NOTE(tssurya): The conflict is due to not having changes
I6f87cf03d49be6bfad2c5e6f0c8accf0fab4e6ee and
Ibd824a77b32cbceb60973a89a93ce09fe6d1050d in Queens.

Change-Id: I0c7b802a453aa423c7273ab724ce78eac0cfed4c
Closes-Bug: #1753833
(cherry picked from commit 8da6831e63)

doc/source/cli/nova-manage.rst

@@ -64,7 +64,8 @@ Nova Database
 
     Move deleted rows from production tables to shadow tables. Note that the
     corresponding rows in the instance_mappings and request_specs tables of the
-    API database are purged when instance records are archived. Specifying
+    API database are purged when instance records are archived and thus,
+    CONF.api_database.connection is required in the config file. Specifying
     --verbose will print the results of the archive operation for any tables that
     were changed. Specifying --until-complete will make the command run
     continuously until all deleted rows are archived. Use the --max_rows option,

nova/cmd/manage.py

@@ -497,7 +497,8 @@ Error: %s""") % six.text_type(e))
         """Move deleted rows from production tables to shadow tables.
 
         Returns 0 if nothing was archived, 1 if some number of rows were
-        archived, 2 if max_rows is invalid. If automating, this should be
+        archived, 2 if max_rows is invalid, 3 if no connection could be
+        established to the API DB. If automating, this should be
         run continuously while the result is 1, stopping at 0.
         """
         max_rows = int(max_rows)
@@ -509,6 +510,19 @@ Error: %s""") % six.text_type(e))
                   {'max_value': db.MAX_INT})
             return 2
 
+        ctxt = context.get_admin_context()
+        try:
+            # NOTE(tssurya): This check has been added to validate if the API
+            # DB is reachable or not as this is essential for purging the
+            # instance_mappings and request_specs of the deleted instances.
+            objects.CellMappingList.get_all(ctxt)
+        except db_exc.CantStartEngineError:
+            print(_('Failed to connect to API DB so aborting this archival '
+                    'attempt. Please check your config file to make sure that '
+                    'CONF.api_database.connection is set and run this '
+                    'command again.'))
+            return 3
+
         table_to_rows_archived = {}
         deleted_instance_uuids = []
         if until_complete and verbose:
@@ -527,7 +541,6 @@ Error: %s""") % six.text_type(e))
             if deleted_instance_uuids:
                 table_to_rows_archived.setdefault('instance_mappings', 0)
                 table_to_rows_archived.setdefault('request_specs', 0)
-                ctxt = context.get_admin_context()
                 deleted_mappings = objects.InstanceMappingList.destroy_bulk(
                                             ctxt, deleted_instance_uuids)
                 table_to_rows_archived['instance_mappings'] += deleted_mappings

nova/tests/unit/test_nova_manage.py

@@ -388,7 +388,9 @@ class DBCommandsTestCase(test.NoDBTestCase):
 
     @mock.patch.object(db, 'archive_deleted_rows',
                        return_value=(dict(instances=10, consoles=5), list()))
-    def _test_archive_deleted_rows(self, mock_db_archive, verbose=False):
+    @mock.patch.object(objects.CellMappingList, 'get_all')
+    def _test_archive_deleted_rows(self, mock_get_all, mock_db_archive,
+                                   verbose=False):
         result = self.commands.archive_deleted_rows(20, verbose=verbose)
         mock_db_archive.assert_called_once_with(20)
         output = self.output.getvalue()
@@ -415,7 +417,9 @@ class DBCommandsTestCase(test.NoDBTestCase):
         self._test_archive_deleted_rows(verbose=True)
 
     @mock.patch.object(db, 'archive_deleted_rows')
-    def test_archive_deleted_rows_until_complete(self, mock_db_archive,
+    @mock.patch.object(objects.CellMappingList, 'get_all')
+    def test_archive_deleted_rows_until_complete(self, mock_get_all,
+                                                 mock_db_archive,
                                                  verbose=False):
         mock_db_archive.side_effect = [
             ({'instances': 10, 'instance_extra': 5}, list()),
@@ -447,7 +451,9 @@ Archiving.....complete
         self.test_archive_deleted_rows_until_complete(verbose=False)
 
     @mock.patch.object(db, 'archive_deleted_rows')
-    def test_archive_deleted_rows_until_stopped(self, mock_db_archive,
+    @mock.patch.object(objects.CellMappingList, 'get_all')
+    def test_archive_deleted_rows_until_stopped(self, mock_get_all,
+                                                mock_db_archive,
                                                 verbose=True):
         mock_db_archive.side_effect = [
             ({'instances': 10, 'instance_extra': 5}, list()),
@@ -479,7 +485,9 @@ Archiving.....stopped
         self.test_archive_deleted_rows_until_stopped(verbose=False)
 
     @mock.patch.object(db, 'archive_deleted_rows', return_value=({}, []))
-    def test_archive_deleted_rows_verbose_no_results(self, mock_db_archive):
+    @mock.patch.object(objects.CellMappingList, 'get_all')
+    def test_archive_deleted_rows_verbose_no_results(self, mock_get_all,
+                                                     mock_db_archive):
         result = self.commands.archive_deleted_rows(20, verbose=True)
         mock_db_archive.assert_called_once_with(20)
         output = self.output.getvalue()
@@ -534,6 +542,21 @@ Archiving.....stopped
         else:
             self.assertEqual(0, len(output))
 
+    @mock.patch.object(objects.CellMappingList, 'get_all',
+                       side_effect=db_exc.CantStartEngineError)
+    def test_archive_deleted_rows_without_api_connection_configured(self,
+                                                           mock_get_all):
+        result = self.commands.archive_deleted_rows(20, verbose=True)
+        mock_get_all.assert_called_once()
+        output = self.output.getvalue()
+        expected = '''\
+Failed to connect to API DB so aborting this archival attempt. \
+Please check your config file to make sure that CONF.api_database.connection \
+is set and run this command again.
+'''
+        self.assertEqual(expected, output)
+        self.assertEqual(3, result)
+
     @mock.patch.object(migration, 'db_null_instance_uuid_scan',
                        return_value={'foo': 0})
     def test_null_instance_uuid_scan_no_records_found(self, mock_scan):