Add nova-manage cell_v2 create_cell command

Currently, all of the commands that create a new cell require the
presence of compute hosts, else they won't create a cell mapping.
In the use case of a fresh install, it's reasonable that compute
host records may not yet exist at the time of cells v2 setup.

This provides a way for operators to create a new empty cell at
setup time and defer adding hosts to the cell until they have
started their compute hosts later (via the 'discover_hosts'
command).

The command optionally accepts a database connection url and
message queue transport url, else it will take the values from
the nova.conf. It returns the uuid of the newly created cell.

Change-Id: I2fd7d854ffa579e550f6002cfb7223d7f40acac6
Related-Bug: #1656276

nova/cmd/manage.py

@@ -103,6 +103,7 @@ _EXTRA_DEFAULT_LOG_LEVELS = ['oslo_db=INFO', 'oslo_policy=INFO']
 
 # Decorators for actions
 args = cmd_common.args
+action_description = cmd_common.action_description
 
 
 def param2id(object_id):
@@ -1397,6 +1398,49 @@ class CellV2Commands(object):
                         cell_mapping=cell_mapping)
                     host_mapping.create()
 
+    @action_description(
+        _("Add a new cell to nova API database. "
+          "DB and MQ urls can be provided directly "
+          "or can be taken from config. The result is cell uuid."))
+    @args('--name', metavar='<name>', help=_('The name of the cell'))
+    @args('--database_connection', metavar='<database url>',
+          dest='database_connection',
+          help=_('The database url for the cell database'))
+    @args('--transport-url', metavar='<transport url>', dest='transport_url',
+          help=_('The transport url for the cell message queue'))
+    @args('--verbose', action='store_true',
+          help=_('Output the uuid of the created cell'))
+    def create_cell(self, name=None, database_connection=None,
+                    transport_url=None, verbose=False):
+        ctxt = context.get_context()
+        transport_url = transport_url or CONF.transport_url
+        if not transport_url:
+            print(_('Must specify --transport-url if [DEFAULT]/transport_url '
+                    'is not set in the configuration file.'))
+            return 1
+        database_connection = database_connection or CONF.database.connection
+        if not database_connection:
+            print(_('Must specify --database_connection '
+                    'if [database]/connection is not set '
+                    'in the configuration file.'))
+            return 1
+        if any(cell.database_connection == database_connection
+               and cell.transport_url == transport_url
+               for cell in objects.CellMappingList.get_all(ctxt)):
+            print(_('Cell with the specified transport_url '
+                    'and database_connection combination already exists'))
+            return 2
+        cell_mapping_uuid = uuidutils.generate_uuid()
+        cell_mapping = objects.CellMapping(
+            ctxt,
+            uuid=cell_mapping_uuid, name=name,
+            transport_url=transport_url,
+            database_connection=database_connection)
+        cell_mapping.create()
+        if verbose:
+            print(cell_mapping_uuid)
+        return 0
+
 
 CATEGORIES = {
     'account': AccountCommands,

nova/tests/unit/test_nova_manage.py

@@ -1370,6 +1370,62 @@ class CellV2CommandsTestCase(test.NoDBTestCase):
         self.assertEqual(from_cli,
                          self.commands._validate_transport_url(from_cli))
 
+    def test_create_cell_use_params(self):
+        ctxt = context.get_context()
+        kwargs = dict(
+            name='fake-name',
+            transport_url='fake-transport-url',
+            database_connection='fake-db-connection')
+        status = self.commands.create_cell(verbose=True, **kwargs)
+        self.assertEqual(0, status)
+        cell2_uuid = self.output.getvalue().strip()
+        self.commands.create_cell(**kwargs)
+        cell2 = objects.CellMapping.get_by_uuid(ctxt, cell2_uuid)
+        self.assertEqual(kwargs['name'], cell2.name)
+        self.assertEqual(kwargs['database_connection'],
+                         cell2.database_connection)
+        self.assertEqual(kwargs['transport_url'], cell2.transport_url)
+
+    def test_create_cell_use_config_values(self):
+        settings = dict(
+            transport_url='fake-conf-transport-url',
+            database_connection='fake-conf-db-connection')
+        self.flags(connection=settings['database_connection'],
+                   group='database')
+        self.flags(transport_url=settings['transport_url'])
+        ctxt = context.get_context()
+
+        status = self.commands.create_cell(verbose=True)
+        self.assertEqual(0, status)
+        cell1_uuid = self.output.getvalue().strip()
+        cell1 = objects.CellMapping.get_by_uuid(ctxt, cell1_uuid)
+        self.assertIsNone(cell1.name)
+        self.assertEqual(settings['database_connection'],
+                         cell1.database_connection)
+        self.assertEqual(settings['transport_url'], cell1.transport_url)
+
+    def test_create_cell_failed_if_non_unique(self):
+        kwargs = dict(
+            name='fake-name',
+            transport_url='fake-transport-url',
+            database_connection='fake-db-connection')
+        status1 = self.commands.create_cell(verbose=True, **kwargs)
+        status2 = self.commands.create_cell(verbose=True, **kwargs)
+        self.assertEqual(0, status1)
+        self.assertEqual(2, status2)
+        self.assertIn('exists', self.output.getvalue())
+
+    def test_create_cell_failed_if_no_transport_url(self):
+        status = self.commands.create_cell()
+        self.assertEqual(1, status)
+        self.assertIn('--transport-url', self.output.getvalue())
+
+    def test_create_cell_failed_if_no_database_connection(self):
+        self.flags(connection=None, group='database')
+        status = self.commands.create_cell(transport_url='fake-transport-url')
+        self.assertEqual(1, status)
+        self.assertIn('--database_connection', self.output.getvalue())
+
 
 class TestNovaManageMain(test.NoDBTestCase):
     """Tests the nova-manage:main() setup code."""