So i did this (my blog) and discovered my example network config did not transfer. Eventually i ended up with a config command of
And it returned to working order, Debian 8 did not appear to need that.
A full example
iface eth0 inet dhcp
iface lo inet loopback
allow-hotplug eth0:1 #<needed per instance
iface eth0:1 inet static
I added back the the dhcp licence which the debian installer also removed. Oh also watch out for /etc/default/networking.