When processing port events (create, update, delete), the port
provisioning (port creation) has priority over the other events [1].
As reported in the related bug, if a port deletion with an IP
address and another port creation with the same IP address arrive
to the DHCP agent, those events can be processed in the same queue.
Because of the creation event priority, even when this event arrived
after the deletion event, it will be processed first. That will
clash with the DHCP agent cache, that contains a port (not deleted
yet) with the same IP address. That will trigger an unwanted resync.
This patch implements a specific logic to store the events in
"ResourceProcessingQueue" (that uses "PriorityQueue" [2]). When
a port event arrives, the event comparison method checks the
(subnet, fixed_ips) tuple set of both elements. If there is a
coincidence, that means those ports are the same or are using
the same IP addreses (the race condition explained in the bug).
In this case, the priority is defined only by the timestamp;
that means the events are processed in order of arrival.
Because the Neutron server do not allow to have two ports in the
same subnet with the same IP address, the order of the events is
guaranteed. In the case explained in the bug, the deletion event
will be processed first.
[1]https://review.opendev.org/c/openstack/neutron/+/626830
[2]https://docs.python.org/3/library/queue.html#queue.PriorityQueue
Closes-Bug: #1913723
Conflicts:
neutron/agent/dhcp/agent.py
neutron/tests/unit/agent/dhcp/test_agent.py
Change-Id: I89438feae3c0244f6da5e6a2a035d45b956ac247
(cherry picked from commit f3c229b9cc)
e753dad6bf