Comment 4 for bug 1922891

Netplan will configure a list of nameservers per interface, as well as the defaults which end up rendered in /etc/resolv.conf. MAAS configures netplan's default nameservers as the nameservers configured for the default gateway's interface. When the default gateway is not explicitly set, after bond interfaces and bridge interfaces, the boot interface is the preferred default.

A POST to /MAAS/api/2.0/nodes/{system_id}/interfaces/{id}/?op=set_default_gateway, will configure the provided interface's default link's subnet as the default gateway. The associated nameservers will then be the default nameservers.