Support large network queries towards neutron

While querying metadata from an LB source, the subnet query may result
with a large number of networks.
That might exceed the maximum request length on the following port query
towards Neutron.
The patch addresses such issue.

Closes-Bug: #1861087
Change-Id: I9d72c80574d08d8409ed0dcc0476f52a0d173a1e

nova/api/metadata/handler.py

@@ -39,6 +39,12 @@ from nova.network import neutron as neutronapi
 CONF = nova.conf.CONF
 LOG = logging.getLogger(__name__)
 
+# 160 networks is large enough to satisfy most cases.
+# Yet while reaching 182 networks Neutron server will break as URL length
+# exceeds the maximum. Left this at 160 to allow additional parameters when
+# they're needed.
+MAX_QUERY_NETWORKS = 160
+
 
 class MetadataRequestHandler(wsgi.Application):
     """Serve metadata."""
@@ -219,11 +225,14 @@ class MetadataRequestHandler(wsgi.Application):
 
         try:
             # Retrieve the instance data from the instance's port
-            ports = neutron.list_ports(
-                context,
-                fixed_ips='ip_address=' + instance_address,
-                network_id=md_networks,
-                fields=['device_id', 'tenant_id'])['ports']
+            ports = []
+            while md_networks:
+                ports.extend(neutron.list_ports(
+                    context,
+                    fixed_ips='ip_address=' + instance_address,
+                    network_id=md_networks[:MAX_QUERY_NETWORKS],
+                    fields=['device_id', 'tenant_id'])['ports'])
+                md_networks = md_networks[MAX_QUERY_NETWORKS:]
         except Exception as e:
             LOG.error('Failed to get instance id for metadata '
                       'request, provider %(provider)s '

nova/tests/unit/test_metadata.py

@@ -1400,6 +1400,45 @@ class MetadataHandlerTestCase(test.TestCase):
 
         self.assertEqual(200, response.status_int)
 
+    @mock.patch.object(neutronapi, 'get_client', return_value=mock.Mock())
+    def test_metadata_lb_proxy_many_networks(self, mock_get_client):
+
+        def fake_list_ports(context, fixed_ips, network_id, fields):
+            if 'f-f-f-f' in network_id:
+                return {'ports':
+                            [{'device_id': 'a-b-c-d', 'tenant_id': 'test'}]}
+            return {'ports': []}
+
+        self.flags(service_metadata_proxy=True, group='neutron')
+        handler.MAX_QUERY_NETWORKS = 10
+
+        self.expected_instance_id = b'a-b-c-d'
+
+        # with X-Metadata-Provider
+        proxy_lb_id = 'edge-x'
+
+        mock_client = mock_get_client.return_value
+        subnet_list = [{'network_id': 'f-f-f-' + chr(c)}
+                       for c in range(ord('a'), ord('z'))]
+        mock_client.list_subnets.return_value = {
+            'subnets': subnet_list}
+
+        with mock.patch.object(
+                mock_client, 'list_ports',
+                side_effect=fake_list_ports) as mock_list_ports:
+
+            response = fake_request(
+                self, self.mdinst,
+                relpath="/2009-04-04/user-data",
+                address="192.192.192.2",
+                fake_get_metadata_by_instance_id=self._fake_x_get_metadata,
+                headers={'X-Forwarded-For': '192.192.192.2',
+                         'X-Metadata-Provider': proxy_lb_id})
+
+            self.assertEqual(3, mock_list_ports.call_count)
+
+        self.assertEqual(200, response.status_int)
+
     @mock.patch.object(neutronapi, 'get_client', return_value=mock.Mock())
     def _metadata_handler_with_provider_id(self, hnd, mock_get_client):
         # with X-Metadata-Provider