Make "enabled_drivers" config option more resilient to failures

Do not fail to start the ironic-conductor service if there's a
trailing comma or an empty value as part of the "enabled_drivers" or
"enabled_network_interfaces" configuration option, instead, log a warning
alerting the operation of the wrong syntax.

Change-Id: Id9141c014263de5e72641613d970fd481a6aaa74
Closes-Bug: #1647783

ironic/common/driver_factory.py

@@ -182,6 +182,13 @@ class BaseDriverFactory(object):
         duplicated_drivers = []
         cls._enabled_driver_list = []
         for item, cnt in counter:
+            if not item:
+                LOG.warning(
+                    _LW('An empty driver was specified in the "%s" '
+                        'configuration option and will be ignored. Please '
+                        'fix your ironic.conf file to avoid this warning '
+                        'message.'), cls._enabled_driver_list_config_option)
+                continue
             if cnt > 1:
                 duplicated_drivers.append(item)
             cls._enabled_driver_list.append(item)

ironic/tests/unit/common/test_driver_factory.py

@@ -71,6 +71,14 @@ class DriverLoadTestCase(base.TestCase):
             ['fake'], driver_factory.DriverFactory._extension_manager.names())
         self.assertTrue(mock_log.called)
 
+    @mock.patch.object(driver_factory.LOG, 'warning', autospec=True)
+    def test_driver_empty_entry(self, mock_log):
+        self.config(enabled_drivers=['fake', ''])
+        driver_factory.DriverFactory._init_extension_manager()
+        self.assertEqual(
+            ['fake'], driver_factory.DriverFactory._extension_manager.names())
+        self.assertTrue(mock_log.called)
+
     @mock.patch.object(driver_factory, '_warn_if_unsupported')
     def test_driver_init_checks_unsupported(self, mock_warn):
         self.config(enabled_drivers=['fake'])

releasenotes/notes/error-resilient-enabled_drivers-4e9c864ed6eaddd1.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - Fixes an issue where the ironic-conductor service would not
+    run if a trailing comma or empty driver was specified in the
+    ``[DEFAULT]enabled_drivers`` configuration option. The service now
+    runs and logs a warning.