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> We currently have a single network node in our deployment, we need to upgrade it to 10gb
> So I thought, I would add a second network node and do a swing migration and thus avoid an outage.
>
> Is this possible in havana ? Whats the process to do it ?

Yes and no.
Yes, you can migrate the l3 node to a different machine but no, it will not be 100% instantaneous.
Depending on how many networks are connected to the l3 agent it will take some time for each of those to be up & running although it will probably be running again within a minute.
I would certainly not do this without announcing some kind of maintenance window.. 

The steps depend a bit on the configuration.
I would not do this without doing a test with a dev setup first so you get comfortable with how this works.
Do not forget that the l3 agent is also NATing for floating IPs and the metadata agent so make sure that also keeps working.
( usually it entails running "neutron l3-agent-router-remove $AGENTID $ROUTERID"  which should be schedule the router on a new l3 node.
Depending on if you use namespaces or not you will have to make sure the router_id in the l3_agent.ini on the new node is properly set to the same id)

Cheers,
Robert van Leeuwen