Fix LB failover when IP addresses exhausted

When a load balancer failover was performed on a load balancer where
the VIP address is on a subnet that has no IP addresses available,
the VIP address may be deactivated.
This patch corrects the failover flow to not deallocate the VIP
address on a failover revert flow due to the subnet being out of
IP addresses.

Story: 2008625
Task: 41827
Change-Id: I1fe342d2bdf1301dd89ab7dfaa8e6a23e69c252b
(cherry picked from commit e3ab49c60a)

octavia/controller/worker/v1/flows/load_balancer_flows.py

@@ -420,8 +420,8 @@ class LoadBalancerFlows(object):
 
         # Check that the VIP port exists and is ok
         failover_LB_flow.add(
-            network_tasks.AllocateVIP(requires=constants.LOADBALANCER,
+            network_tasks.AllocateVIPforFailover(
-                                      provides=constants.VIP))
+                requires=constants.LOADBALANCER, provides=constants.VIP))
 
         # Update the database with the VIP information
         failover_LB_flow.add(database_tasks.UpdateVIPAfterAllocation(

octavia/controller/worker/v1/tasks/network_tasks.py

@@ -462,6 +462,20 @@ class AllocateVIP(BaseNetworkTask):
                       {'vip': vip.ip_address, 'except': e})
 
 
+class AllocateVIPforFailover(AllocateVIP):
+    """Task to allocate/validate the VIP for a failover flow."""
+
+    def revert(self, result, loadbalancer, *args, **kwargs):
+        """Handle a failure to allocate vip."""
+
+        if isinstance(result, failure.Failure):
+            LOG.exception("Unable to allocate VIP")
+            return
+        vip = result
+        LOG.info("Failover revert is not deallocating vip %s because this is "
+                 "a failover.", vip.ip_address)
+
+
 class DeallocateVIP(BaseNetworkTask):
     """Task to deallocate a VIP."""
 

octavia/tests/unit/controller/worker/v1/tasks/test_network_tasks.py

@@ -716,6 +716,22 @@ class TestNetworkTasks(base.TestCase):
         net.revert(vip_mock, LB)
         mock_driver.deallocate_vip.assert_called_once_with(vip_mock)
 
+    def test_allocate_vip_for_failover(self, mock_get_net_driver):
+        mock_driver = mock.MagicMock()
+        mock_get_net_driver.return_value = mock_driver
+        net = network_tasks.AllocateVIPforFailover()
+
+        mock_driver.allocate_vip.return_value = LB.vip
+
+        mock_driver.reset_mock()
+        self.assertEqual(LB.vip, net.execute(LB))
+        mock_driver.allocate_vip.assert_called_once_with(LB)
+
+        # revert
+        vip_mock = mock.MagicMock()
+        net.revert(vip_mock, LB)
+        mock_driver.deallocate_vip.assert_not_called()
+
     def test_deallocate_vip(self, mock_get_net_driver):
         mock_driver = mock.MagicMock()
         mock_get_net_driver.return_value = mock_driver

releasenotes/notes/Fix-failover-ip-addresses-exhausted-69110b2fa4683e1a.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes an issue with load balancer failover, when the VIP subnet is out of
+    IP addresses, that could lead to the VIP being deallocated.