Comment 30 for bug 1711760

I have reviewed this. +1 from ~ubuntu-sru.

Regression risk is mitigated as Scott says by careful gating of the active code to limit exposure of these changes to the non-default use case only.

I did note the following:

What happens when the DHCP lease acquired in the initramfs expires? What if the DNS server changes after a new lease? Really it's the entire DHCP lease that needs handing over from the initramfs rather than just the DNS server that was provided at the time of the first lease on boot. But this will only affect this impacted non-default use case. If this doesn't matter for you, then fine. If it does, then please mark verification-failed and we can go again with a fix that will cover this case.

If not on systemd and inside a container, check will not work. We don't support !systemd on Ubuntu, so that should be OK. We may be on upstart after upgrading from Trusty; in that case the /proc/cmdline gate should still work so this will only affect systems booted this way using MAAS on Trusty and then upgraded to Xenial until next reboot.

Adding a udev rule that is a shell script for every network up and down. How does this effect udev, for example on a system with a large number of flapping interfaces? On a quick glance I didn't see any other shell script udev rule on such a wide reaching trigger.

Any race conditions before is-from-initrd gate, for example if multiple interfaces come up close together in time? I don't see any.

Please make sure to test that the gating is working correctly in the non-kernel-cmdline case during SRU verification.