Make RPCFixture support multiple connections

For testing cells, we will need to track the driver instances that
we give out by url. This normally just works with a conventional
oslo.messaging driver, but the fake driver keeps internal data
structures for simulating its bus. If we end up with clients creating
a new instance of the driver in the rpc switching code, we'll never
be able to send messages to services because we'll always have
private/separate data structures.

So, this makes the fixture wrap the transport creation stuff
and unify references by url. In order to make this work, some
retooling of rpc.init() is done, which makes it more in line with
the recent additions we had for wrapping transport initialization
per connection anyway.

For now, a lot of our tests can't handle the possibility of
multiple RPC connections due to them looking at the global
transport_url configuration. So for the moment, even though this
makes the fixture support multiple independent connections, we
collapse any such attempts down to a single connection to the
default broker.

Note: this requires a fix in oslo.messaging 5.14.0

Depends-On: I01b6f5a20ea9752da46a546a908bd38cf11da681
Change-Id: Icb63d7dabd17f3c5633387793f68a8ba20863a7e

nova/tests/fixtures.py

@@ -27,6 +27,7 @@ import mock
 from oslo_concurrency import lockutils
 from oslo_config import cfg
 from oslo_db.sqlalchemy import enginefacade
+import oslo_messaging as messaging
 from oslo_messaging import conffixture as messaging_conffixture
 import six
 
@@ -495,6 +496,27 @@ class RPCFixture(fixtures.Fixture):
         super(RPCFixture, self).__init__()
         self.exmods = []
         self.exmods.extend(exmods)
+        self._buses = {}
+
+    def _fake_create_transport(self, url):
+        # FIXME(danms): Right now, collapse all connections
+        # to a single bus. This is how our tests expect things
+        # to work. When the tests are fixed, this fixture can
+        # support simulating multiple independent buses, and this
+        # hack should be removed.
+        url = None
+
+        # NOTE(danms): This will be called with a non-None url by
+        # cells-aware code that is requesting to contact something on
+        # one of the many transports we're multplexing here.
+        if url not in self._buses:
+            exmods = rpc.get_allowed_exmods()
+            self._buses[url] = messaging.get_transport(
+                CONF,
+                url=url,
+                allowed_remote_exmods=exmods,
+                aliases=rpc.TRANSPORT_ALIASES)
+        return self._buses[url]
 
     def setUp(self):
         super(RPCFixture, self).setUp()
@@ -504,7 +526,15 @@ class RPCFixture(fixtures.Fixture):
         self.messaging_conf = messaging_conffixture.ConfFixture(CONF)
         self.messaging_conf.transport_driver = 'fake'
         self.useFixture(self.messaging_conf)
-        rpc.init(CONF)
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.rpc.create_transport', self._fake_create_transport))
+        # NOTE(danms): Execute the init with get_transport_url() as None,
+        # instead of the parsed TransportURL(None) so that we can cache
+        # it as it will be called later if the default is requested by
+        # one of our mq-switching methods.
+        with mock.patch('nova.rpc.get_transport_url') as mock_gtu:
+            mock_gtu.return_value = None
+            rpc.init(CONF)
 
 
 class WarningsFixture(fixtures.Fixture):

requirements.txt

@@ -43,7 +43,7 @@ oslo.serialization>=1.10.0 # Apache-2.0
 oslo.utils>=3.18.0 # Apache-2.0
 oslo.db!=4.13.1,!=4.13.2,>=4.11.0 # Apache-2.0
 oslo.rootwrap>=5.0.0 # Apache-2.0
-oslo.messaging>=5.2.0 # Apache-2.0
+oslo.messaging>=5.14.0 # Apache-2.0
 oslo.policy>=1.17.0 # Apache-2.0
 oslo.privsep>=1.9.0 # Apache-2.0
 oslo.i18n>=2.1.0 # Apache-2.0