Comment 3 for bug 1998621

Reviewed: https://review.opendev.org/c/openstack/neutron/+/866489
Committed: https://opendev.org/openstack/neutron/commit/74224e79e031636018b970fac9c2aa72516eb12d
Submitter: "Zuul (22348)"
Branch: master

commit 74224e79e031636018b970fac9c2aa72516eb12d
Author: Sebastian Lohff <email address hidden>
Date: Fri Dec 2 17:36:44 2022 +0100

    Gracefully restart dnsmasq to not break tcp DNS

    When talking to dnsmasq using DNS over tcp dnsmasq will fork out for
    TCP connections. Forked processes will stay until all connections have
    been closed, meaning that dangling connections will keep the processes
    and with that will also keep the tcp/53 port in listening state. On
    dnsmasq restart (e.g. on network update, subnet create, ...) the parent
    process is killed with SIGKILL and a new process is started. This new
    process cannot listen on tcp/53, as it is still in use by the old child
    with the dangling connection.

    To prevent dangling dnsmasq connections on tcp we need to properly
    shutdown the child. This is done by first sending SIGTERM and only send
    a SIGKILL if the process is not shutting down properly. With that we
    get proper cleanup of all children and tcp will come up after a restart.

    Change-Id: Ie633148c512f5124e978648c50a4c6318c61baa8
    Closes-bug: #1998621