Make versioned notifications topics configurable

Some services (such as telemetry) actually consume the notifications.
If one deploys a service that listens on the same queue as telemetry,
there will be race-conditions with these services and one will not get
the notifications that are expected at points.

To address this, one sets a different topic and consumes from there.
This is not possible with versioned notifications at the moment. And, as
services move towards using them, the same need will arise.

This adds a configuration option to Ironic enabling the configuration
of topics for this notifier.

A similar change was introduced in nova:
https://review.openstack.org/#/c/444947/

Change-Id: Ib75feac0979d0094cb137abb13b0fe0ff4576eee
Story: 2004735
Task: 28788

doc/source/admin/notifications.rst

@@ -60,6 +60,11 @@ field of the payload. Consumers are guaranteed that microversion bumps will add
 new fields, while macroversion bumps are backwards-incompatible and may have
 fields removed.
 
+Versioned notifications are emitted by default to the
+`ironic_versioned_notifications` topic. This can be changed and it is
+configurable in the ironic.conf with the `versioned_notifications_topics`
+config option.
+
 Available notifications
 =======================
 .. TODO(mariojv) Add some form of tabular formatting below

ironic/common/rpc.py

@@ -13,17 +13,15 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from oslo_config import cfg
 import oslo_messaging as messaging
 from oslo_messaging.rpc import dispatcher
 from osprofiler import profiler
 
 from ironic.common import context as ironic_context
 from ironic.common import exception
+from ironic.conf import CONF
 
 
-CONF = cfg.CONF
-
 TRANSPORT = None
 NOTIFICATION_TRANSPORT = None
 SENSORS_NOTIFIER = None
@@ -53,10 +51,10 @@ def init(conf):
                                                 serializer=serializer,
                                                 driver='noop')
     else:
-        VERSIONED_NOTIFIER = messaging.Notifier(NOTIFICATION_TRANSPORT,
-                                                serializer=serializer,
-                                                topics=['ironic_versioned_'
-                                                        'notifications'])
+        VERSIONED_NOTIFIER = messaging.Notifier(
+            NOTIFICATION_TRANSPORT,
+            serializer=serializer,
+            topics=CONF.versioned_notifications_topics)
 
 
 def cleanup():

ironic/conf/default.py

@@ -238,10 +238,11 @@ netconf_opts = [
                       '"127.0.0.1".')),
 ]
 
-# NOTE(mariojv) By default, accessing this option when it's unset will return
-# None, indicating no notifications will be sent. oslo.config returns None by
-# default for options without set defaults that aren't required.
 notification_opts = [
+    # NOTE(mariojv) By default, accessing this option when it's unset will
+    # return None, indicating no notifications will be sent. oslo.config
+    # returns None by default for options without set defaults that aren't
+    # required.
     cfg.StrOpt('notification_level',
                choices=[('debug', _('"debug" level')),
                         ('info', _('"info" level')),
@@ -250,7 +251,22 @@ notification_opts = [
                         ('critical', _('"critical" level'))],
                help=_('Specifies the minimum level for which to send '
                       'notifications. If not set, no notifications will '
-                      'be sent. The default is for this option to be unset.'))
+                      'be sent. The default is for this option to be unset.')),
+    cfg.ListOpt(
+        'versioned_notifications_topics',
+        default=['ironic_versioned_notifications'],
+        help=_("""
+Specifies the topics for the versioned notifications issued by Ironic.
+
+The default value is fine for most deployments and rarely needs to be changed.
+However, if you have a third-party service that consumes versioned
+notifications, it might be worth getting a topic for that service.
+Ironic will send a message containing a versioned notification payload to each
+topic queue in this list.
+
+The list of versioned notifications is visible in
+https://docs.openstack.org/ironic/latest/admin/notifications.html
+""")),
 ]
 
 path_opts = [

ironic/tests/unit/common/test_rpc.py

@@ -48,9 +48,24 @@ class TestUtils(base.TestCase):
                                 mock_get_notification, mock_json_serializer,
                                 mock_notifier)
 
-    def _test_init_globals(self, notifications_enabled, mock_get_rpc_transport,
-                           mock_get_notification, mock_json_serializer,
-                           mock_notifier):
+    @mock.patch.object(messaging, 'Notifier', autospec=True)
+    @mock.patch.object(messaging, 'JsonPayloadSerializer', autospec=True)
+    @mock.patch.object(messaging, 'get_notification_transport', autospec=True)
+    @mock.patch.object(messaging, 'get_rpc_transport', autospec=True)
+    def test_init_globals_with_custom_topics(self, mock_get_rpc_transport,
+                                             mock_get_notification,
+                                             mock_json_serializer,
+                                             mock_notifier):
+        self._test_init_globals(
+            False, mock_get_rpc_transport, mock_get_notification,
+            mock_json_serializer, mock_notifier,
+            versioned_notifications_topics=['custom_topic1', 'custom_topic2'])
+
+    def _test_init_globals(
+            self, notifications_enabled, mock_get_rpc_transport,
+            mock_get_notification, mock_json_serializer, mock_notifier,
+            versioned_notifications_topics=['ironic_versioned_notifications']):
+
         rpc.TRANSPORT = None
         rpc.NOTIFICATION_TRANSPORT = None
         rpc.SENSORS_NOTIFIER = None
@@ -89,7 +104,7 @@ class TestUtils(base.TestCase):
                 mock.call(
                     rpc.NOTIFICATION_TRANSPORT,
                     serializer=mock_request_serializer.return_value,
-                    topics=['ironic_versioned_notifications'])
+                    topics=versioned_notifications_topics)
             ]
 
         mock_notifier.assert_has_calls(notifier_calls)

releasenotes/notes/make-versioned-notifications-topics-configurable-18d70d573c27809e.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Adds a ``[DEFAULT]/versioned_notifications_topics`` configuration option.
+    This enables operators to configure the topics used for versioned
+    notifications.