Merge ~mpontillo/maas:prevent-ip-removal-on-bridge-release--bug-1792409 into maas:master

[Mike Pontillo]

LP #1792409 - Prevent removal of IP addresses when bridge interfaces are removed on release.

This was a strange race condition that seems to be related to the Django result cache - logging suggested that it was finding IP addresses attached to interfaces, when those IP addresses had been previously removed moments earlier.

Invalidating the cache didn't work, but we already had a workaround in the signal handler we could use to prevent the unwanted deletion of any IP addresses.

bfefc48... by Mike Pontillo on 2018-10-18

LP: #1792409 - Prevent removal of IP addresses when bridge interfaces are removed on release.

[Mike Pontillo (mpontillo)]

Note: I couldn't find a good way to unit test this change, since it's a race condition that we don't see in that environment, and I can't access the same instance of the BridgeInterface to make sure it has the _skip_ip_address_removal attribute set.

[MAAS Lander (maas-lander)]

UNIT TESTS
-b prevent-ip-removal-on-bridge-release--bug-1792409 lp:~mpontillo/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: SUCCESS
COMMIT: bfefc4842bfd0d35bd7f9251b1f41565545f6e77

review: Approve

[Alberto Donato (ack)]

lgtm

review: Approve

diff --git a/src/maasserver/models/node.py b/src/maasserver/models/node.py
index c44ec3c..e1fc47b 100644
--- a/src/maasserver/models/node.py
+++ b/src/maasserver/models/node.py
@@ -3282,7 +3282,11 @@ class Node(CleanSave, TimestampedModel):
                 for sip in interface.ip_addresses.all():
                     sip.interface_set.remove(interface)
                     sip.interface_set.add(parent)
-                # Delete the acquired bridge interface.
+                # Delete the acquired bridge interface, and set a property
+                # to prevent a race condition that would otherwise cause
+                # the IP addresses moved to the physical interface to be
+                # deleted.
+                setattr(interface, '_skip_ip_address_removal', True)
                 interface.delete()
 
     def _clear_networking_configuration(self):