[Openstack-operators] [openstack-dev] [nova] [placement] extraction (technical) update

Mohammed Naser mnaser at vexxhost.com
Thu Sep 6 12:33:44 UTC 2018

On Wed, Sep 5, 2018 at 12:41 PM Dan Smith <dms at danplanet.com> wrote:
> > I think there was a period in time where the nova_api database was created
> > where entires would try to get pulled out from the original nova database and
> > then checking nova_api if it doesn't exist afterwards (or vice versa).  One
> > of the cases that this was done to deal with was for things like instance types
> > or flavours.
> >
> > I don't know the exact details but I know that older instance types exist in
> > the nova db and the newer ones are sitting in nova_api.  Something along
> > those lines?
> Yep, we've moved entire databases before in nova with minimal disruption
> to the users. Not just flavors, but several pieces of data came out of
> the "main" database and into the api database transparently. It's
> doable, but with placement being split to a separate
> project/repo/whatever, there's not really any option for being graceful
> about it in this case.
> > At this point, I'm thinking turn off placement, setup the new one, do
> > the migration
> > of the placement-specific tables (this can be a straightforward documented task
> > OR it would be awesome if it was a placement command (something along
> > the lines of `placement-manage db import_from_nova`) which would import all
> > the right things
> >
> > The idea of having a command would be *extremely* useful for deployment tools
> > in automating the process and it also allows the placement team to selectively
> > decide what they want to onboard?
> Well, it's pretty cut-and-dried as all the tables in nova-api are either
> for nova or placement, so there's not much confusion about what belongs.
> I'm not sure that doing this import in python is really the most
> efficient way. I agree a placement-manage command would be ideal from an
> "easy button" point of view, but I think a couple lines of bash that
> call mysqldump are likely to vastly outperform us doing it natively in
> python. We could script exec()s of those commands from python, but.. I
> think I'd rather just see that as a shell script that people can easily
> alter/test on their own.
> Just curious, but in your case would the service catalog entry change at
> all? If you stand up the new placement in the exact same spot, it
> shouldn't, but I imagine some people will have the catalog entry change
> slightly (even if just because of a VIP or port change). Am I
> remembering correctly that the catalog can get cached in various places
> such that much of nova would need a restart to notice?

We already have placement in the catalog and it's behind a load balancer
so changing the backends resolves things right away, so we likely won't
be needing any restarts (and I don't think OSA will either because it uses
the same model).

> --Dan

Mohammed Naser — vexxhost
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E. mnaser at vexxhost.com
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