[ovs-discuss] active_backup failover issue

[Francois]

> > On Tue, 27 Apr 2021 at 23:08, Numan Siddique <numans at ovn.org> wrote:

> > > Having 3 chassis will not result in this split brain scenario which you have
> > > probably observed.

I dig a little deeper. I guess what I experience is an issue when only having 2
chassis hosting gateways.

ha_chassis_group_is_active reads

    if (sset_is_empty(active_tunnels)) {
        /* If active tunnel sset is empty, it means it has lost
         * connectivity with other chassis. */
        return false;
    }

I think the code tries to prevent a split brain scenario here: if
there is no tunnel working it necessarily means the current chassis is broken
(although there should be a tunnel working towards a compute).

When there are 2 chassis in the group, when the first chassis goes down, the
only tunnel is down, and the port is never claimed. I can solve that by having
3 chassis in the group or returning true  (when a_ch_grp->n_ha_chassis == 2)
above.

I don't think practically anyone would run with only 2 chassis acting as gateway
though!

Thanks
Francois