Start metadata proxy even if IPv6 DAD fails

A recent change suppressed the IPv6 DAD failure and
removed the address when multiple DHCP agents were
configured on the same network,
https://review.opendev.org/c/openstack/neutron/+/880957

But it also changed the behavior to not enable IPv4
metadata in this case. Restore the old behavior by
not returning early in the DAD failure case. The callback
that builds the config file was moved until after
the address was bound to make the two steps more obvious.

Conflicts:
    neutron/tests/unit/agent/metadata/test_driver.py

Related-bug: #1953165
Change-Id: I8436c6c9da9a2533ca27ff7312f5b2c7ea41e94f
(cherry picked from commit 846003c)
(cherry picked from commit e7f85ab)
(cherry picked from commit 1a711f3)

Author: brianphaley

neutron/agent/metadata/driver.py

@@ -255,14 +255,6 @@ def spawn_monitored_metadata_proxy(cls, monitor, ns_name, port, conf,
                                        bind_address="0.0.0.0", network_id=None,
                                        router_id=None, bind_address_v6=None,
                                        bind_interface=None):
-        uuid = network_id or router_id
-        callback = cls._get_metadata_proxy_callback(
-            bind_address, port, conf,
-            network_id=network_id, router_id=router_id,
-            bind_address_v6=bind_address_v6, bind_interface=bind_interface)
-        pm = cls._get_metadata_proxy_process_manager(uuid, conf,
-                                                     ns_name=ns_name,
-                                                     callback=callback)
         if bind_interface is not None and bind_address_v6 is not None:
             # HAProxy cannot bind() until IPv6 Duplicate Address Detection
             # completes. We must wait until the address leaves its 'tentative'
@@ -290,7 +282,18 @@ def spawn_monitored_metadata_proxy(cls, monitor, ns_name, port, conf,
                 except Exception as exc:
                     # do not re-raise a delete failure, just log
                     LOG.info('Address deletion failure: %s', str(exc))
-                return
+
+                # Do not use the address or interface when DAD fails
+                bind_address_v6 = bind_interface = None
+
+        uuid = network_id or router_id
+        callback = cls._get_metadata_proxy_callback(
+            bind_address, port, conf,
+            network_id=network_id, router_id=router_id,
+            bind_address_v6=bind_address_v6, bind_interface=bind_interface)
+        pm = cls._get_metadata_proxy_process_manager(uuid, conf,
+                                                     ns_name=ns_name,
+                                                     callback=callback)
         pm.enable()
         monitor.register(uuid, METADATA_SERVICE_NAME, pm)
         cls.monitors[router_id] = pm

neutron/tests/unit/agent/metadata/test_driver.py

@@ -176,9 +176,12 @@ def _test_spawn_metadata_proxy(self, dad_failed=False):
                 "%s.conf" % router_id)
             mock_open = self.useFixture(
                 lib_fixtures.OpenFixture(cfg_file)).mock_open
+            bind_v6_line = 'bind %s:%s interface %s' % (
+                self.METADATA_DEFAULT_IPV6, self.METADATA_PORT, 'fake-if')
             if dad_failed:
                 mock_wait.side_effect = ip_lib.DADFailed(
-                    address=self.METADATA_DEFAULT_IP, reason='DAD failed')
+                    address=self.METADATA_DEFAULT_IPV6, reason='DAD failed')
+                bind_v6_line = ''
             else:
                 mock_wait.return_value = True
             agent.metadata_driver.spawn_monitored_metadata_proxy(
@@ -197,8 +200,6 @@ def _test_spawn_metadata_proxy(self, dad_failed=False):
 
             log_tag = ("haproxy-" + metadata_driver.METADATA_SERVICE_NAME +
                        "-" + router_id)
-            bind_v6_line = 'bind %s:%s interface %s' % (
-                self.METADATA_DEFAULT_IPV6, self.METADATA_PORT, 'fake-if')
             cfg_contents = metadata_driver._HAPROXY_CONFIG_TEMPLATE % {
                 'user': self.EUNAME,
                 'group': self.EGNAME,
@@ -214,26 +215,26 @@ def _test_spawn_metadata_proxy(self, dad_failed=False):
                 'bind_v6_line': bind_v6_line}
 
             if dad_failed:
-                agent.process_monitor.register.assert_not_called()
                 mock_del.assert_called_once_with(self.METADATA_DEFAULT_IPV6,
                                                  'fake-if',
                                                  namespace=router_ns)
             else:
-                mock_open.assert_has_calls([
-                    mock.call(cfg_file, 'w'),
-                    mock.call().write(cfg_contents)], any_order=True)
-
-                ip_mock.assert_has_calls([
-                    mock.call(namespace=router_ns),
-                    mock.call().netns.execute(netns_execute_args,
-                                              addl_env=None, run_as_root=True)
-                ])
-
-                agent.process_monitor.register.assert_called_once_with(
-                    router_id, metadata_driver.METADATA_SERVICE_NAME,
-                    mock.ANY)
                 mock_del.assert_not_called()
 
+            mock_open.assert_has_calls([
+                mock.call(cfg_file, 'w'),
+                mock.call().write(cfg_contents)], any_order=True)
+
+            ip_mock.assert_has_calls([
+                mock.call(namespace=router_ns),
+                mock.call().netns.execute(netns_execute_args, addl_env=None,
+                                          run_as_root=True)
+            ])
+
+            agent.process_monitor.register.assert_called_once_with(
+                router_id, metadata_driver.METADATA_SERVICE_NAME,
+                mock.ANY)
+
     def test_spawn_metadata_proxy(self):
         self._test_spawn_metadata_proxy()