Ephemeral boot has broken DNS

[Mark Shuttleworth]

I am seeing consistent failures in hardware testing, because 'failed to install dependencies'. Digging into that, it seems that all ephemeral boots are getting an empty resolv.conf.

There is a reasonably sensible looking /etc/network/interfaces.d/50-cloud-init.cfg :

iface enp1s0 inet dhcp
    broadcast 192.168.9.255
    dns-nameservers 192.168.9.10
    gateway 192.168.9.1

Something is going wrong in either the DHCP piece or the writing of /etc/resolv.conf though, because:

ubuntu@amused-guinea:~$ 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
ubuntu@amused-guinea:~$

Interestingly, if I run dhclient manually, this seems to fix itself, but there are no dhclient entries in syslog before I run it manually.