If MAAS has ipv4 and ipv6 subnets present on a vlan with dhcp enabled, and the maas_url is set to an ipv6 address, dns generation fails as below. This should not be a traceback, and hopefully should at least produce a partially-working DNS.
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 return func(*args, **kwds)
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 File "/usr/lib/python3/dist-packages/maasserver/dhcp.py", line 565, in get_dhcp_configuration
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 default_domain, dhcp_snippets)
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 File "/usr/lib/python3/dist-packages/maasserver/dhcp.py", line 451, in get_dhcp_configure_for
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 rack_controller, ipv4=(ip_version == 4), ipv6=(ip_version == 6))
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 File "/usr/lib/python3/dist-packages/maasserver/dns/zonegenerator.py", line 119, in get_dns_server_address
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 iplist = get_dns_server_addresses(rack_controller, ipv4, ipv6)
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 File "/usr/lib/python3/dist-packages/maasserver/dns/zonegenerator.py", line 150, in get_dns_server_addresses
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011 % e.strerror)
Sep 30 22:05:47 maas-boot-vm-xenial sh[20078]: #011maasserver.dns.zonegenerator.DNSException: Unable to find MAAS server IP address: Address family for hostname not supported. MAAS's DNS server requires this IP address for the NS records in its zone files. Make sure that the configuration setting for the MAAS URL has the correct hostname. Consult the 'maas-region local_config_set --maas-url' command.
As I think about this, what we're trying to do is find the IP of the rack, so that we can give it to the DHCPing node to use for name resolution... It should be raised as an error, somehow.