Comment 2 for bug 2056366

Reviewed: https://review.opendev.org/c/openstack/neutron/+/911625
Committed: https://opendev.org/openstack/neutron/commit/a4e49b6b8fcf9acfa4e84c65de19ffd56b9022e7
Submitter: "Zuul (22348)"
Branch: master

commit a4e49b6b8fcf9acfa4e84c65de19ffd56b9022e7
Author: Terry Wilson <email address hidden>
Date: Wed Mar 6 20:13:58 2024 +0000

    Use oslo_service's SignalHandler for signals

    When Neutron is killed with SIGTERM (like via systemctl), when using
    ML2/OVN neutron workers do not exit and instead are eventually killed
    with SIGKILL when the graceful timeout is reached (often around 1
    minute).

    This is happening due to the signal handlers for SIGTERM. There are
    multiple issues.

    1) oslo_service, ml2/ovn mech_driver, and ml2/ovo_rpc.py all call
       signal.signal(signal.SIGTERM, ...) overwriting each others signal
       handlers.
    2) SIGTERM is handled in the main thread, and running blocking code
       there causes AssertionErrors in eventlet which also prevents the
       process from exiting.
    3) The ml2/ovn cleanup code doesn't cause the process to end, so it
       interrupts the killing of the process.

    oslo_service has a singleton SignalHandler class that solves all of
    these issues

    Closes-Bug: #2056366
    Depends-On: https://review.opendev.org/c/openstack/oslo.service/+/911627
    Change-Id: I730a12746bceaa744c658854e38439420efc4629
    Signed-off-by: Terry Wilson <email address hidden>