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I'm running Icehouse with the 'legacy' nova-network service and a single 
network node.

Everything in my cluster is running Ubuntu Trusty and ready for an 
upgrade to Juno, except for my network node, which is still running 
Precise.  How do I upgrade it without causing cloud-wide downtime? I can 
think of a few approaches, none of which I feel confident about undertaking:

1: Build a new network node running Trusty, and then nudge existing VMs 
off of the old node and onto the new one.  I've gotten fairly far down 
this path, but just realized that I don't have any idea how to do the 
'nudge' step.

2: Switch my network to multi-node mode, add a new network node, somehow 
inform VMs about the new secondary node, then upgrade and reboot network 
nodes one at a time and rely on the instances to fail over to the 
running node during upgrade.

3: Stop having special-purpose network nodes altogether and adopt the 
(more-modern, as I understand it) approach of running nova-network on 
each compute node.  This seems ideal in the long run, but also maximize 
the amount of tinkering and potential disaster.

Has anyone done this?  #2 seems like the obvious approach since it gets 
me some redundancy in the long run, but I'm not at all clear on what the 
steps are given an already-running-and-useful network.  I have the 
feeling that I've read a guide about upgrade-via-migration which would 
closely resemble #1 but I can no longer find that document.

Thank you!

-Andrew