Add strict option to discover_hosts

This adds a --strict option that can be passed in when calling the
nova-manage cell_v2 discover_hosts command. When this option is used,
the command will only return success if a new host has been found.
In any other case it is considered a failure.

Closes-Bug: #1692982

Change-Id: I942af11a3987e1edce67423c66931ad9ece65587

doc/source/man/nova-manage.rst

@@ -143,14 +143,17 @@ Nova Cells v2
     transport url or database connection was missing, and 2 if a cell is
     already using that transport url and database connection combination.
 
-``nova-manage cell_v2 discover_hosts [--cell_uuid <cell_uuid>] [--verbose]``
+``nova-manage cell_v2 discover_hosts [--cell_uuid <cell_uuid>] [--verbose] [--strict]``
 
     Searches cells, or a single cell, and maps found hosts. This command will
     check the database for each cell (or a single one if passed in) and map
     any hosts which are not currently mapped. If a host is already mapped
     nothing will be done. You need to re-run this command each time you add
     more compute hosts to a cell (otherwise the scheduler will never place
-    instances there and the API will not list the new hosts).
+    instances there and the API will not list the new hosts). If the strict
+    option is provided the command will only be considered successful if an
+    unmapped host is discovered (exit code 0). Any other case is considered a
+    failure (exit code 1).
 
 ``nova-manage cell_v2 list_cells [--verbose]``
 

nova/cmd/manage.py

@@ -1448,7 +1448,11 @@ class CellV2Commands(object):
                'map.')
     @args('--verbose', action='store_true',
           help=_('Provide detailed output when discovering hosts.'))
-    def discover_hosts(self, cell_uuid=None, verbose=False):
+    @args('--strict', action='store_true',
+          help=_('Considered successful (exit code 0) only when an unmapped '
+                 'host is discovered. Any other outcome will be considered a '
+                 'failure (exit code 1).'))
+    def discover_hosts(self, cell_uuid=None, verbose=False, strict=False):
         """Searches cells, or a single cell, and maps found hosts.
 
         When a new host is added to a deployment it will add a service entry
@@ -1461,7 +1465,10 @@ class CellV2Commands(object):
                 print(msg)
 
         ctxt = context.RequestContext()
-        host_mapping_obj.discover_hosts(ctxt, cell_uuid, status_fn)
+        hosts = host_mapping_obj.discover_hosts(ctxt, cell_uuid, status_fn)
+        # discover_hosts will return an empty list if no hosts are discovered
+        if strict:
+            return int(not hosts)
 
     @action_description(
         _("Add a new cell to nova API database. "

nova/tests/unit/test_nova_manage.py

@@ -1390,6 +1390,19 @@ class CellV2CommandsTestCase(test.NoDBTestCase):
 
         mock_cell_mapping_get_by_uuid.assert_not_called()
 
+    @mock.patch('nova.objects.host_mapping.discover_hosts')
+    def test_discover_hosts_strict(self, mock_discover_hosts):
+        # Check for exit code 0 if unmapped hosts found
+        mock_discover_hosts.return_value = ['fake']
+        self.assertEqual(self.commands.discover_hosts(strict=True), 0)
+
+        # Check for exit code 1 if no unmapped hosts are found
+        mock_discover_hosts.return_value = []
+        self.assertEqual(self.commands.discover_hosts(strict=True), 1)
+
+        # Check the return when strict=False
+        self.assertIsNone(self.commands.discover_hosts())
+
     def test_validate_transport_url_in_conf(self):
         from_conf = 'fake://user:pass@host:port/'
         self.flags(transport_url=from_conf)