[Openstack] Upgrade nova-network without downtime?

Andrew Bogott abogott at wikimedia.org
Mon Aug 3 14:17:05 UTC 2015

On 7/28/15 1:32 PM, Andrew Bogott wrote:
> 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.
> <snip>
It turns out that I now need to do rolling restarts of my compute nodes 
for an unrelated issue (see: "kvm suspend vs. the kernel") so I have a 
bit more leeway with this problem.  After a bit of reading I'm convinced 
that while I'm messing with things it's probably a good idea to switch 
to multi_host anyway.  So, I propose the following steps:

1) Install nova-network on all compute nodes
2) nova-network delete (current network setting)
3) nova-network create (same network settings as in step 2 except with 
multi_host on)
4) restart nova-network on all compute nodes

My supposition is that after doing that, old instances will continue to 
use my old, standalone network node (as specified in their cached dhcp 
settings) until they are restarted at which point they'll switch over to 
using their local compute host as a router thanks to the multi_host setting.

Can anyone confirm that this is a sensible plan, or warn me off of it?  
The main danger I see is that at that after step 2, nova-compute 
probably can't be safely restarted on my original compute node -- that's 
definitely a bit fragile :(


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