[openstack-dev] [TripleO] Migration from Neutron ML2OVS to OVN

Ben Nemec openstack at nemebean.com
Tue Jul 11 18:10:12 UTC 2017

On 07/11/2017 10:17 AM, Numan Siddique wrote:
> Hello Tripleo team,
> I have few questios regarding migration from neutron ML2OVS to OVN. 
> Below are some of the requirements
>   - We want to migrate an existing depoyment from Neutroon default 
>   - We are targetting this for tripleo Queen's release.
>   - The plan is to first upgrade the tripleo deployment from Pike to 
> Queens with no changes to neutron. i.e with neutron ML2OVS. Once the 
> upgrade is done, we want to migrate to OVN.
>   - The migration process will stop all the neutron agents, configure 
> neutron server to load OVN mechanism driver and start OVN services (with 
> no or very limited datapath downtime).
>   - The migration would be handled by an ansible script. We have a PoC 
> ansible script which can be found here [1]
> And the questions are
> -  (A broad question) - What is the right way to migrate and switch the 
> neutron plugin ? Can the stack upgrade handle the migration as well ?
> - The migration procedure should be part of tripleo ? or can it be a 
> standalone ansible script ? (I presume it should be former).
> - If it should be part of the tripleo then what would be the command to 
> do it ? A update stack command with appropriate environment files for OVN ?
> - In case the migration can be done  as a standalone script, how to 
> handle later updates/upgrades since tripleo wouldn't be aware of the 
> migration ?

This last point seems like the crux of the discussion here.  Sure, you 
can do all kinds of things to your cloud using standalone bits, but if 
any of them affect things tripleo manages (which this would) then you're 
going to break on the next stack update.

If there are things about the migration that a stack-update can't 
handle, then the migration process would need to be twofold: 1) Run the 
standalone bits to do the migration 2) Update the tripleo configuration 
to match the migrated config so stack-updates work.

This is obviously a complex and error-prone process, so I'd strongly 
encourage doing it in a tripleo-native fashion instead if at all possible.

> Request to provide your comments so that we can move in the right direction.
> [1] - https://github.com/openstack/networking-ovn/tree/master/migration
> Thanks
> Numan
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