Fix nova-metadata-api for ovn dhcp native networks

With the change from ml2/ovs DHCP agents towards OVN implementation
in neutron there is no port with device_owner network:dhcp anymore.
Instead DHCP is provided by network:distributed port.

Closes-Bug: 2055245
Change-Id: Ibb569b9db1475b8bbd8f8722d49228182cd47f85
(cherry picked from commit 135af52)
(cherry picked from commit 45a9261)

Author: Steven Blatzheim

nova/network/neutron.py

@@ -3610,6 +3610,7 @@ def _get_subnets_from_port(self, context, port, client=None):
                            'gateway': network_model.IP(
                                 address=subnet['gateway_ip'],
                                 type='gateway'),
+                           'enable_dhcp': False,
             }
             if subnet.get('ipv6_address_mode'):
                 subnet_dict['ipv6_address_mode'] = subnet['ipv6_address_mode']
@@ -3626,22 +3627,14 @@ def _get_subnets_from_port(self, context, port, client=None):
                         subnet_dict['dhcp_server'] = ip_pair['ip_address']
                         break
 
-            # NOTE(arnaudmorin): If enable_dhcp is set on subnet, but, for
-            # some reason neutron did not have any DHCP port yet, we still
-            # want the network_info to be populated with a valid dhcp_server
-            # value. This is mostly useful for the metadata API (which is
-            # relying on this value to give network_data to the instance).
-            #
-            # This will also help some providers which are using external
-            # DHCP servers not handled by neutron.
-            # In this case, neutron will never create any DHCP port in the
-            # subnet.
-            #
-            # Also note that we cannot set the value to None because then the
-            # value would be discarded by the metadata API.
-            # So the subnet gateway will be used as fallback.
-            if subnet.get('enable_dhcp') and 'dhcp_server' not in subnet_dict:
-                subnet_dict['dhcp_server'] = subnet['gateway_ip']
+            # NOTE(stblatzheim): If enable_dhcp is set on subnet, but subnet
+            # has ovn native dhcp and no dhcp-agents. Network owner will be
+            # network:distributed
+            # Just rely on enable_dhcp flag given by neutron
+            # Fix for https://bugs.launchpad.net/nova/+bug/2055245
+
+            if subnet.get('enable_dhcp'):
+                subnet_dict['enable_dhcp'] = True
 
             subnet_object = network_model.Subnet(**subnet_dict)
             for dns in subnet.get('dns_nameservers', []):

nova/tests/unit/network/test_neutron.py

@@ -3615,8 +3615,8 @@ def test_get_subnets_from_port_enabled_dhcp_no_dhcp_ports(self,
 
         subnets = self.api._get_subnets_from_port(self.context, port_data)
 
-        self.assertEqual(subnet_data1[0]['gateway_ip'],
-                         subnets[0]['meta']['dhcp_server'])
+        self.assertEqual(subnet_data1[0]['enable_dhcp'],
+                         subnets[0]['meta']['enable_dhcp'])
 
     @mock.patch.object(neutronapi, 'get_client', return_value=mock.Mock())
     def test_get_physnet_tunneled_info_multi_segment(self, mock_get_client):

nova/virt/netutils.py

@@ -289,7 +289,8 @@ def _get_nets(vif, subnet, version, net_num, link_id):
     net_type = ''
     if subnet.get_meta('ipv6_address_mode') is not None:
         net_type = '_%s' % subnet.get_meta('ipv6_address_mode')
-    elif subnet.get_meta('dhcp_server') is not None:
+    elif (subnet.get_meta('dhcp_server') is not None or
+          subnet.get_meta('enable_dhcp')):
         net_info = {
             'id': 'network%d' % net_num,
             'type': 'ipv%d_dhcp' % version,

releasenotes/notes/bug-2055245-fix-nova-metadata-api-f60b18b1b594bec0.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    With the change from ml2/ovs DHCP agents towards OVN implementation
+    in neutron there is no port with device_owner ``network:dhcp`` anymore.
+    Instead DHCP is provided by ``network:distributed`` port.
+    Fix relies on enable_dhcp provided by neutron-api if no port with
+    ``network:dhcp`` owner is found. See `bug 2055245
+    <https://bugs.launchpad.net/nova/+bug/2055245>`__ for details.