Fail if required extensions are missing

If the required extensions are missing, we currently log an error
that is going to be practically ignored. That said, the unfulfilled
requirement will most definitely going to lead to other failures,
so we might as well fail fast.

This patch also cleans up some <barf>dns-integration nonsense</barf>
within the ML2 framework: the extension must not be declared statically
as it's being loaded by the extension manager, and this fixes the lousy
unit tests we have to live with. As for the db base plugin, some cleanup
is still overdue, but it will have to be taken care of in a follow-up
patch.

Closes-bug: #1538623

Change-Id: Id50eeb52c5d209170042b48821a29af3421c2f5c

doc/source/devref/effective_neutron.rst

@@ -74,6 +74,11 @@ Document common pitfalls as well as good practices done during plugin developmen
 * When adding behavior to the L2 and L3 db base classes, do not assume that
   there is an agent on the other side of the message broker that interacts
   with the server. Plugins may not rely on `agents <https://review.openstack.org/#/c/174020/>`_ at all.
+* Be mindful of required capabilities when you develop plugin extensions. The
+  `Extension description <https://github.com/openstack/neutron/blob/master/neutron/api/extensions.py#L122>`_ provides the ability to specify the list of required capabilities
+  for the extension you are developing. By declaring this list, the server will
+  not start up if the requirements are not met, thus avoiding leading the system
+  to experience undetermined behavior at runtime.
 
 Database interaction
 ~~~~~~~~~~~~~~~~~~~~

neutron/api/extensions.py

@@ -440,10 +440,11 @@ class ExtensionManager(object):
                 # Exit loop as no progress was made
                 break
         if exts_to_process:
-            # NOTE(salv-orlando): Consider whether this error should be fatal
             LOG.error(_LE("It was impossible to process the following "
                           "extensions: %s because of missing requirements."),
                       ','.join(exts_to_process.keys()))
+            raise exceptions.ExtensionsNotFound(
+                extensions=list(exts_to_process.keys()))
 
         # Extending extensions' attributes map.
         for ext in processed_exts.values():

neutron/db/db_base_plugin_v2.py

@@ -1172,7 +1172,8 @@ class NeutronDbPluginV2(db_base_plugin_common.DbBasePluginCommon,
                          status=p.get('status', constants.PORT_STATUS_ACTIVE),
                          device_id=p['device_id'],
                          device_owner=p['device_owner'])
-        if 'dns_name' in p:
+        if ('dns-integration' in self.supported_extension_aliases and
+            'dns_name' in p):
             request_dns_name = self._get_request_dns_name(p)
             port_data['dns_name'] = request_dns_name
 
@@ -1190,13 +1191,15 @@ class NeutronDbPluginV2(db_base_plugin_common.DbBasePluginCommon,
 
             ips = self.ipam.allocate_ips_for_port_and_store(context, port,
                                                             port_id)
-            if 'dns_name' in p:
+            if ('dns-integration' in self.supported_extension_aliases and
+                'dns_name' in p):
                 dns_assignment = []
                 if ips:
                     dns_assignment = self._get_dns_names_for_port(
                         context, ips, request_dns_name)
 
-        if 'dns_name' in p:
+        if ('dns-integration' in self.supported_extension_aliases and
+            'dns_name' in p):
             db_port['dns_assignment'] = dns_assignment
         return self._make_port_dict(db_port, process_extensions=False)
 

neutron/plugins/ml2/plugin.py

@@ -125,7 +125,7 @@ class Ml2Plugin(db_base_plugin_v2.NeutronDbPluginV2,
                                     "multi-provider", "allowed-address-pairs",
                                     "extra_dhcp_opt", "subnet_allocation",
                                     "net-mtu", "vlan-transparent",
-                                    "address-scope", "dns-integration",
+                                    "address-scope",
                                     "availability_zone",
                                     "network_availability_zone"]
 

neutron/tests/unit/api/test_extensions.py

@@ -502,6 +502,13 @@ class RequestExtensionTest(base.BaseTestCase):
 
 class ExtensionManagerTest(base.BaseTestCase):
 
+    def test_missing_required_extensions(self):
+        ext_mgr = extensions.ExtensionManager('')
+        attr_map = {}
+        ext_mgr.add_extension(ext_stubs.StubExtensionWithReqs('foo_alias'))
+        self.assertRaises(exceptions.ExtensionsNotFound,
+                          ext_mgr.extend_resources, "2.0", attr_map)
+
     def test_invalid_extensions_are_not_registered(self):
 
         class InvalidExtension(object):

neutron/tests/unit/db/test_agentschedulers_db.py

@@ -1400,8 +1400,7 @@ class OvsAgentSchedulerTestCase(OvsAgentSchedulerTestCaseBase):
                                                  exc.HTTPNotFound.code)
 
 
-class OvsDhcpAgentNotifierTestCase(test_l3.L3NatTestCaseMixin,
-                                   test_agent.AgentDBTestMixIn,
+class OvsDhcpAgentNotifierTestCase(test_agent.AgentDBTestMixIn,
                                    AgentSchedulerTestMixIn,
                                    test_plugin.NeutronDbPluginV2TestCase):
     plugin_str = 'neutron.plugins.ml2.plugin.Ml2Plugin'

neutron/tests/unit/extension_stubs.py

@@ -37,6 +37,12 @@ class StubExtension(extensions.ExtensionDescriptor):
         return ""
 
 
+class StubExtensionWithReqs(StubExtension):
+
+    def get_required_extensions(self):
+        return ["foo"]
+
+
 class StubPlugin(object):
 
     def __init__(self, supported_extensions=None):

releasenotes/notes/fail-on-missing-extensions-bc332124b780875b.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - The server will fail to start if any of the declared required
+    extensions, as needed by core and service plugins, are not
+    properly configured.