Remove dead code of api.fault notification sending

Based on the description of the notify_on_api_faults config option [1]
and the code that uses it [2] nova sends and api.fault notification
if the nova-api service encounters an unhandle exception.
There is a FaultWrapper class [3] added to the  pipeline of the REST
request which catches every exception and calls the notification sending.

Based on some debugging in devstack this FaultWrapper never catches any
exception. Every REST API method is decorated with expected_errors
decorator [5] which as a last resort translate the unexpected exception
to HTTPInternalServerError. In the wsgi stack the actual REST api call is
guarded with ResourceExceptionHandler context manager [7] which translates
HTTPException to a Fault [8]. Then Fault is catched and translated to
the REST response [7]. This way the exception never propagates back to
the FaultWrapper and therefore the api.fault notification is never emitted.

Based on the git history of the expected_errors decorator this notification
was never emitted for v2.1 API and as the v2.0 API now supported with the
same codebase than v2.1 it is not emitted for v2.0 calls either. As nobody
reported a bug I assume that nobody tried to use this notification for a very
long time. Therefore instead of fixing this bug this patch propses to remove
the dead code.

See a bit more detailed description on the ML [9].

[1] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/conf/notifications.py#L49
[2] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/notifications/base.py#L84
[3] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/api/openstack/__init__.py#L78
[5] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/api/openstack/extensions.py#L325
[7] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/api/openstack/wsgi.py#L637
[8] https://github.com/openstack/nova/blob/0aeaa2bce8ad15bc2f28e00b30d688514b992e13/nova/api/openstack/wsgi.py#L418
[9] http://lists.openstack.org/pipermail/openstack-dev/2017-June/118639.html

Change-Id: I608b6ebdc69d31eb2a11ac6479fa4f2e8c20f7d1
Closes-Bug: #1699115

doc/source/reference/notifications.rst

@@ -41,7 +41,7 @@ Notifier object depends on the parameters of the get_notifier call and the
 value of the oslo.messaging configuration options `driver` and `topics`.
 There are notification configuration options in Nova which are specific for
 certain notification types like `notifications.notify_on_state_change`,
-`notifications.notify_on_api_faults`, `notifications.default_level`, etc.
+`notifications.default_level`, etc.
 
 The structure of the payload of the unversioned notifications is defined in the
 code that emits the notification and no documentation or enforced backward

nova/api/openstack/__init__.py

@@ -26,7 +26,6 @@
 from nova.api.openstack import wsgi
 import nova.conf
 from nova.i18n import translate
-from nova import notifications
 from nova import utils
 from nova import wsgi as base_wsgi
 
@@ -75,7 +74,6 @@ def _error(self, inner, req):
             outer.explanation = '%s: %s' % (inner.__class__.__name__,
                                             inner_msg)
 
-        notifications.send_api_fault(req.url, status, inner)
         return wsgi.Fault(outer)
 
     @webob.dec.wsgify(RequestClass=wsgi.Request)

nova/conf/notifications.py

@@ -43,16 +43,6 @@
 * None - no notifications
 * "vm_state" - notifications on VM state changes
 * "vm_and_task_state" - notifications on VM and task state changes
-"""),
-
-    cfg.BoolOpt(
-        'notify_on_api_faults',
-        default=False,
-        deprecated_group='DEFAULT',
-        deprecated_name='notify_api_faults',
-        help="""
-If enabled, send api.fault notifications on caught exceptions in the
-API service.
 """),
 
     cfg.StrOpt(

nova/notifications/__init__.py

@@ -22,6 +22,5 @@
 from nova.notifications.base import image_meta  # noqa
 from nova.notifications.base import info_from_instance  # noqa
 from nova.notifications.base import notify_decorator  # noqa
-from nova.notifications.base import send_api_fault  # noqa
 from nova.notifications.base import send_update  # noqa
 from nova.notifications.base import send_update_with_states  # noqa

nova/notifications/base.py

@@ -24,7 +24,6 @@
 from oslo_log import log
 from oslo_utils import excutils
 from oslo_utils import timeutils
-import six
 
 import nova.conf
 import nova.context
@@ -81,21 +80,6 @@ def wrapped_func(*args, **kwarg):
     return wrapped_func
 
 
-def send_api_fault(url, status, exception):
-    """Send an api.fault notification."""
-
-    if not CONF.notifications.notify_on_api_faults:
-        return
-
-    payload = {'url': url, 'exception': six.text_type(exception),
-               'status': status}
-
-    rpc.get_notifier('api').error(common_context.get_current() or
-                                  nova.context.get_admin_context(),
-                                  'api.fault',
-                                  payload)
-
-
 def send_update(context, old_instance, new_instance, service="compute",
                 host=None):
     """Send compute.instance.update notification to report any changes occurred

nova/rpc.py

@@ -260,7 +260,6 @@ class LegacyValidatingNotifier(object):
         'aggregate.updatemetadata.start',
         'aggregate.updateprop.end',
         'aggregate.updateprop.start',
-        'api.fault',
         'compute.instance.create.end',
         'compute.instance.create.error',
         'compute.instance.create_ip.end',

nova/tests/unit/test_notifications.py

@@ -99,97 +99,6 @@ def _wrapped_create(self, params=None):
         inst.create()
         return inst
 
-    def test_send_api_fault_disabled(self):
-        self.flags(notify_on_api_faults=False, group='notifications')
-        notifications.send_api_fault("http://example.com/foo", 500, None)
-        self.assertEqual(0, len(fake_notifier.NOTIFICATIONS))
-
-    def test_send_api_fault(self):
-        self.flags(notify_on_api_faults=True, group='notifications')
-        exception = None
-        try:
-            # Get a real exception with a call stack.
-            raise test.TestingException("junk")
-        except test.TestingException as e:
-            exception = e
-
-        notifications.send_api_fault("http://example.com/foo", 500, exception)
-
-        self.assertEqual(1, len(fake_notifier.NOTIFICATIONS))
-        n = fake_notifier.NOTIFICATIONS[0]
-        self.assertEqual(n.priority, 'ERROR')
-        self.assertEqual(n.event_type, 'api.fault')
-        self.assertEqual(n.payload['url'], 'http://example.com/foo')
-        self.assertEqual(n.payload['status'], 500)
-        self.assertIsNotNone(n.payload['exception'])
-
-    def test_send_api_fault_fresh_context(self):
-        self.flags(notify_on_api_faults=True, group='notifications')
-        exception = None
-        try:
-            # Get a real exception with a call stack.
-            raise test.TestingException("junk")
-        except test.TestingException as e:
-            exception = e
-
-        ctxt = context.RequestContext(overwrite=True)
-        notifications.send_api_fault("http://example.com/foo", 500, exception)
-
-        self.assertEqual(1, len(fake_notifier.NOTIFICATIONS))
-        n = fake_notifier.NOTIFICATIONS[0]
-        self.assertEqual(n.priority, 'ERROR')
-        self.assertEqual(n.event_type, 'api.fault')
-        self.assertEqual(n.payload['url'], 'http://example.com/foo')
-        self.assertEqual(n.payload['status'], 500)
-        self.assertIsNotNone(n.payload['exception'])
-        self.assertEqual(ctxt, n.context)
-
-    def test_send_api_fault_fake_context(self):
-        self.flags(notify_on_api_faults=True, group='notifications')
-        exception = None
-        try:
-            # Get a real exception with a call stack.
-            raise test.TestingException("junk")
-        except test.TestingException as e:
-            exception = e
-
-        ctxt = o_context.get_current()
-        self.assertIsNotNone(ctxt)
-        notifications.send_api_fault("http://example.com/foo", 500, exception)
-
-        self.assertEqual(1, len(fake_notifier.NOTIFICATIONS))
-        n = fake_notifier.NOTIFICATIONS[0]
-        self.assertEqual(n.priority, 'ERROR')
-        self.assertEqual(n.event_type, 'api.fault')
-        self.assertEqual(n.payload['url'], 'http://example.com/foo')
-        self.assertEqual(n.payload['status'], 500)
-        self.assertIsNotNone(n.payload['exception'])
-        self.assertIsNotNone(n.context)
-        self.assertEqual(ctxt, n.context)
-
-    def test_send_api_fault_admin_context(self):
-        self.flags(notify_on_api_faults=True, group='notifications')
-        exception = None
-        try:
-            # Get a real exception with a call stack.
-            raise test.TestingException("junk")
-        except test.TestingException as e:
-            exception = e
-
-        self.fixture._remove_cached_context()
-        self.assertIsNone(o_context.get_current())
-        notifications.send_api_fault("http://example.com/foo", 500, exception)
-
-        self.assertEqual(1, len(fake_notifier.NOTIFICATIONS))
-        n = fake_notifier.NOTIFICATIONS[0]
-        self.assertEqual(n.priority, 'ERROR')
-        self.assertEqual(n.event_type, 'api.fault')
-        self.assertEqual(n.payload['url'], 'http://example.com/foo')
-        self.assertEqual(n.payload['status'], 500)
-        self.assertIsNotNone(n.payload['exception'])
-        self.assertIsNotNone(n.context)
-        self.assertTrue(n.context.is_admin)
-
     def test_notif_disabled(self):
 
         # test config disable of the notifications

releasenotes/notes/api.fault-notification-removal-9f3142ba7cb13ca9.yaml

@@ -0,0 +1,12 @@
+---
+upgrade:
+  - |
+    The ``notify_on_api_faults`` config option and the ``api.fault``
+    notification it enabled have been removed. As noted in `bug 1699115`_,
+    the ``api.fault`` notification has not worked since the v2.1 API was
+    introduced. As the v2.0 API is supported with the v2.1 codebase since
+    Newton, this notification has not been emitted since Newton. Given that
+    no one has reported an issue with this in that time, it is simply
+    removed.
+
+    .. _`bug 1699115`: https://bugs.launchpad.net/nova/+bug/1699115