[OVN] Populate the "router.distributed" flag in ML2/OVN

In ML2/OVN there is a static common configuration parameter to define
if the routers (more in particular the floating IPs) can be distributed
or centralized:
  [ovn] enable_distributed_floating_ip

This patch writes this value on each new router created. It also
implements a maintenance method to populate this flag when the
Neutron API is restarted and the value changed.

Closes-Bug: #2022058
Change-Id: Ib109b09fde4db8738c1d0b3e394c201492d210c6

doc/source/ovn/faq/index.rst

@@ -24,9 +24,10 @@ Frequently Asked Questions
 |               | VRRP traffic.             | tunnel endpoints to detect     |
 |               |                           | connectivity issues to nodes.  |
 +---------------+---------------------------+--------------------------------+
-| DVR           | exposes the "distributed" | no "distributed" flag is shown |
+| DVR           | exposes the "distributed" | exposes the "distributed" flag |
-| API           | flag on routers only      | or available on routers via    |
+| API           | flag on routers only      | based on the configuration     |
-|               | modifiable by admin.      | API.                           |
+|               | modifiable by admin.      | option                         |
+|               |                           | enable_distributed_floating_ip |
 +---------------+---------------------------+--------------------------------+
 | DVR           | uses namespaces, veths,   | Uses OpenFlow rules on the     |
 | dataplane     | ip routing, ip rules and  | compute nodes.                 |

neutron/objects/router.py

@@ -136,6 +136,12 @@ class RouterExtraAttributes(base.NeutronDbObject):
 
         return list(query)
 
+    @classmethod
+    @db_api.CONTEXT_WRITER
+    def update_distributed_flag(cls, context, distributed):
+        query = context.session.query(cls.db_model)
+        query.update({'distributed': distributed})
+
     def obj_make_compatible(self, primitive, target_version):
         _target_version = versionutils.convert_version_to_tuple(target_version)
         if _target_version < (1, 1):

neutron/plugins/ml2/drivers/ovn/mech_driver/ovsdb/maintenance.py

@@ -1095,6 +1095,25 @@ class DBInconsistenciesPeriodics(SchemaAwarePeriodicsBase):
 
         raise periodics.NeverAgain()
 
+    @has_lock_periodic(spacing=86400, run_immediately=True)
+    def update_router_distributed_flag(self):
+        """Set "enable_distributed_floating_ip" on the router.distributed flag.
+
+        This method is needed to sync the static configuration parameter
+        "enable_distributed_floating_ip", loaded when the Neutron API starts,
+        and the router.distributed flag.
+
+        NOTE: remove this method when the RFE that allows to define the
+        distributed flag per FIP is implemented. At this point, the
+        router.distributed flag will be useless.
+            RFE: https://bugs.launchpad.net/neutron/+bug/1978039
+        """
+        distributed = ovn_conf.is_ovn_distributed_floating_ip()
+        router_obj.RouterExtraAttributes.update_distributed_flag(
+            n_context.get_admin_context(), distributed)
+
+        raise periodics.NeverAgain()
+
 
 class HashRingHealthCheckPeriodics(object):
 

neutron/services/ovn_l3/plugin.py

@@ -35,6 +35,7 @@ from neutron._i18n import _
 from neutron.common.ovn import constants as ovn_const
 from neutron.common.ovn import extensions
 from neutron.common.ovn import utils
+from neutron.conf.plugins.ml2.drivers.ovn import ovn_conf
 from neutron.db.availability_zone import router as router_az_db
 from neutron.db import dns_db
 from neutron.db import extraroute_db
@@ -174,6 +175,10 @@ class OVNL3RouterPlugin(service_base.ServicePluginBase,
         context.session.flush()
         router_id = payload.resource_id
         router_db = payload.metadata['router_db']
+        # NOTE(ralonsoh): the "distributed" flag is a static configuration
+        # parameter that needs to be defined only during the router creation.
+        extra_attr = router_db['extra_attributes']
+        extra_attr.distributed = ovn_conf.is_ovn_distributed_floating_ip()
 
         db_rev.create_initial_revision(
             context, router_id, ovn_const.TYPE_ROUTERS,

neutron/tests/unit/objects/test_router.py

@@ -61,6 +61,16 @@ class RouterExtraAttrsDbObjTestCase(obj_test_base.BaseDbObjectTestCase,
         self.update_obj_fields(
             {'router_id': lambda: self._create_test_router_id()})
 
+    def test_update_distributed_flag(self):
+        for obj in self.objs:
+            obj.distributed = False
+            obj.create()
+        router.RouterExtraAttributes.update_distributed_flag(self.context,
+                                                             True)
+        r_e_a_list = router.RouterExtraAttributes.get_objects(self.context)
+        for obj in r_e_a_list:
+            self.assertTrue(obj.distributed)
+
 
 class RouterIfaceObjectTestCase(obj_test_base.BaseObjectIfaceTestCase):
 

releasenotes/notes/ovn-router-distributed-flag-48a8e72c1b258e40.yaml

@@ -0,0 +1,12 @@
+---
+features:
+  - |
+    OVN routers now expose the "distributed" flag depending on the
+    configuration option ``enable_distributed_floating_ip``. Because this is a
+    common configuration option, all routers will expose the same value. This
+    value can flap if the Neutron API is restarted and the configuration option
+    changes.
+    NOTE: Once the RFE that allows us to define the distributed flag per
+    floating IP address is implemented in ML2/OVN, this flag will be useless
+    (no Launchpad bug has been created yet for this RFE, that is only a
+    proposed idea during several PTGs).