Comment 4 for bug 1806777

On bionic iBFT system, I switched to ifupdown:

$ sudo apt install ifupdown
...
$ sudo apt install resolvconf
...
$ sudo apt remove netplan.io
...
$ sudo vi /etc/network/interfaces
...
$ cat /etc/network/interfaces

auto lo
iface lo inet loopback

source /etc/network/interfaces.d/*.cfg

$ sudo update-initramfs -u
...
$ sudo reboot

...[system reboots]...

$ cat /etc/network/interfaces.d/50-cloud-init.cfg
# This file is generated from information provided by
# the datasource. Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
auto lo
iface lo inet loopback

# control-manual ens3f0
iface ens3f0 inet dhcp
    dns-nameservers 169.254.169.254
    gateway 10.0.0.1

$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.

nameserver 169.254.169.254
nameserver 127.0.0.53

So this bug can be reproduced on bionic (and later) by replacing netplan with ifupdown and resolvconf.