Comment 8 for bug 1823314

Reviewed: https://review.openstack.org/651984
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=ee2ed681c495c4fc5086d761853731b7dc2fd34f
Submitter: Zuul
Branch: stable/rocky

commit ee2ed681c495c4fc5086d761853731b7dc2fd34f
Author: Slawek Kaplonski <email address hidden>
Date: Wed Apr 10 12:49:49 2019 +0200

    Choose random value for HA routes' vr_id

    HA routers are using keepalived and needs to have virtual_router_id
    configured. As routers which belongs to same tenant are using same
    ha network, those values have to be different for each router.

    Before this patch this value was always taken as first available value
    from available_vr_ids range.
    In some (rare) cases, when more than one router is created in parallel
    for same tenant it may happen that those routers would have same vr_id
    choosen so keepalived would treat them as single application and only
    one router would be ACTIVE on one of L3 agents.

    This patch changes this behaviour that now random value from available
    vr_ids will be chosen instead of taking first value always.
    That should mittigate this rare race condition that it will be (almost)
    not noticable for users.

    However, proper fix should be probably done as some additional
    constraint in database layer. But such solution wouldn't be possible to
    backport to stable branches so I decided to propose this easy patch
    first.

    Change-Id: Idb0ed744e54976dca23593fb2d7317bf77442e65
    Related-Bug: #1823314
    (cherry picked from commit a8d0f557d504957aeb91f451105cca9eee2d6adb)