Comment 10 for bug 1951149

Reviewed: https://review.opendev.org/c/openstack/neutron/+/839027
Committed: https://opendev.org/openstack/neutron/commit/494cd8ca5dc924dbaa3b3a185110371dfe2e59c1
Submitter: "Zuul (22348)"
Branch: stable/victoria

commit 494cd8ca5dc924dbaa3b3a185110371dfe2e59c1
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Wed Nov 17 17:33:29 2021 +0000

    [OVN] Handle OVN agents when "Chassis" register is deleted

    If an "ovn-controller" ends not gracefully, the node "Chassis" and
    "Chassis_Private" registers will remain in the OVN SB database.
    Because there is no a mandatory procedure to delete the "Chassis"
    and "Chassis_Private" registers, the administrator can manually
    delete, from the OVN SB database, any register in any order.

    If the "Chassis" register is deleted and the Neutron server restarted,
    the updated "Chassis_Private" register will be read from the database.
    That won't contain the "Chassis" information as this register has been
    deleted. In this case, the ``NeutronAgent`` returns ``DeletedChassis``,
    an empty chassis register with no information.

    NOTE: the sequence of actions ("Chassis" register deletion, Neutron
    server restart) must be follow to reproduce this issue. If the
    "Chassis" register is deleted, the Neutron server OVN agent local cache
    won't update the stored information and will keep the previous value.
    It is when the Neutron server is restarted when the OVN agent local
    cache is retrieved again; at this time the "Chassis_Private" register
    won't have any related "Chassis" register.

    Closes-Bug: #1951149

    Conflicts:
      neutron/tests/functional/plugins/ml2/drivers/ovn/mech_driver/test_mech_driver.py

    Change-Id: I17aa53cea6aba8ea83187c99102a6f25fd33cfff
    (cherry picked from commit f1a5511e9094d6aae7a61cd858c59c706033ca95)
    (cherry picked from commit 29998538cec9a696b01d84bd9573f2ebbbb15f90)