Any OVN scheduler, inheriting from ``OVNGatewayScheduler``, calls
``_schedule_gateway`` to make the decision of in what chassis the
router gatweway should be located. Before this patch, if the list
of candidates was empty, the scheduler used all available chassis
as candidate list. This patch is removing this default behaviour.
In a deployment, only those chassis marked explicitly with
"ovn-cms-options=enable-chassis-as-gw" can be used as gateway
chassis.
After enabling this patch, any existing router gateway port will
preserve the assigned chassis; any new router gateway will be
scheduled only on the chassis configured as gateways.
If a router gateway port cannot find any chassis to be scheduled,
the "neutron-ovn-invalid-chassis" will be used instead and a
warning message will be printed in the logs.
Closes-Bug: #2019217
Change-Id: If0f843463edfd7edc5c897cc098de31444f9d81b
413044f253