So from the troubleshooting and testing I just did, it seems like (at least) I had to do the following:
# 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} and mv /etc/netplan/50-cloud-init.yaml /etc/netplan/50-cloud- init.yaml.disabled Before taking these two steps, I kept getting a DHCP address on my interface. After doing this and rebooting, I finally have an interface that is simply "UP" - as configured in my /etc/network/interfaces: # This file describes the network interfaces available on your system # and how to activate them. For more information, see interfaces(5). # The loopback network interface auto lo iface lo inet loopback auto ens160 iface ens160 inet manual -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1771236 Title: forced use of systemd-networkd interferes with ifupdown in 18.04 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1771236/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs