Comment 13 for bug 1750884

Getting this fixed in cloud-init is tricky.
In ifupdown (/etc/network/interfaces) world, we just took the "global dns" entries and put them on the loopback device (lo). Since that device would always be brought up, and never really brought down, it served its purpose.

That is what Ryan tried above, but it doesnt seem to work. Even if it *did* work, the solution would be systemd-networkd specific, and cloud-init doesn't speak to systemd-networkd or systemd-resolved. It speaks to netplan. So we would still need a way for cloud-init to tell netplan to do this.

That leaves us with 2 not-so-great solutions in cloud-init only:
a.) blindly put global dns entries on *all* interfaces
b.) cloud-init search through the config and find the "right" interface to put the global dns entry on.