OVN: DNS resolution not working for instances

[Dr. Jens Harbott]

When using OVN and no explicit nameserver settings are made for a subnet, instances on that subnet will not have working DNS resolution. The reason is that in this case OVN announces the resolver addresses being used on the host to the instances, and with systemd-resolve being used, that address will be 127.0.0.53, which cannot be reasonably used by an instance.

The solution is to specify one or more nameserver addresses in ml2_conf.ini:[ovn]dns_servers, which will then be announced via DHCP instead of the host's nameserver. See also https://bugs.launchpad.net/neutron/+bug/1951074.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Dr. Jens Harbott <email address hidden>" on branch: master
Review: https://review.opendev.org/c/openstack/kolla-ansible/+/818362

[Tom Fifield (fifieldt)]

From the review: " Let's go with not adding this variable at all and just documenting the OVN's behaviour properly (so that operators get to know this detail and how to control it), i.e., show that config override can be used here (it's what we have it for). "