net.ifnames should be set to 0 by default IIUC[1].  It appears that it's
not set in the wily kernel used in this image.  I don't know where we
configure/control the default value.

We don't see this issue with virtio-net nics because systemd considers
virtio numbers to be unstable[2] and doesn't have a rule to name virtio
devices (aka the kernel name get's passed through always).

For e1000, this appears in the systemd database and thus gets renamed
via the default netrules based on slot location (en, slot 3) -> ens3.

If we append 'net.ifnames=0' to the cloud image as of today and use an
e1000 nic, this skips persistent naming and the cloud image boots as
expected.

The trouble occurs when we don't have a nic named eth0 due to persistent
naming rules triggering and the cloud-image has eth0 embedded into it's
filesystem:

% cat /etc/network/interfaces.d/eth0.cfg
# The primary network interface
auto eth0
iface eth0 inet dhcp


1. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762101#105
2. http://lists.freedesktop.org/archives/systemd-devel/2014-July/020908.html


** Bug watch added: Debian Bug tracker #762101
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762101

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https://bugs.launchpad.net/bugs/1483457

Title:
  non-virtio devices get named with systemd "predictable network
  interface names"

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