I think it will be better to redeploy the compute nodes from scratch.
Juno is supported on el7 only.
From my experience with upgrading from 6 to 7, it's a lot of
hassle, 
because the upgrade process only takes care of base the programs.
After the upgrade you will have to upgrade/downgrade/remove manually
the packages that where not updated.
Best regards,
Cristian Falcas
On Tue, Dec 16, 2014 at 6:46 AM, Chris <contact(a)progbau.de> wrote:
 Hello
 We have an relatively big OpenStack setup (> 150 Compute Nodes) based on
 CentOS 6.5 with the RDO Icehouse release.
 We now considering an upgrade to Juno, is there a best practice out there
 how to do it and how is it with the depending CentOS upgrade to 6.6 or even
 7.0?
 Any help is appreciated!
 Thanks,
 Chris
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