[openstack-dev] RFC: Classnames in config parameters harmful to users / upgrades

Doug Hellmann doug.hellmann at dreamhost.com
Wed Feb 6 21:10:23 UTC 2013


On Wed, Feb 6, 2013 at 11:10 AM, Daniel P. Berrange <berrange at redhat.com>wrote:

> On Wed, Feb 06, 2013 at 10:46:52AM -0500, Mark McLoughlin wrote:
> > On Wed, 2013-02-06 at 15:22 +0000, Daniel P. Berrange wrote:
> > > The only way we can do this is if we do *NOT* require the use of
> > > classnames in config parameters. Instead we should treat all these
> > > config parameters as being more like enumerations, and map those to
> > > classnames internally
> > >
> > > eg for the compute_driver instead of having the user set
> > >
> > >   compute_driver=nova.virt.libvirt.LibvirtDriver
> > >
> > > they would do
> > >
> > >   compute_driver=libvirt
> >
> > I think there's already good consensus on this and the idea is to use
> > entry points and stevedore to achieve it.
> >
> > See:
> >
> >   https://blueprints.launchpad.net/nova/+spec/entrypoints-plugins
> >   https://review.openstack.org/11027
> >   https://review.openstack.org/15030
>
> Heh, I've even seen that blueprint before, but it was hard to understand
> just what it was on about. A etherpad transcript of a conversation that
> you weren't present for, doesn't make a nice design doc for blueprint :-(
>

You did a great job of summarizing the issue. Could you find a way to add
that information to the blueprint? Maybe start a wiki page to replace the
etherpad, include your summary and the link to the etherpad?

Doug


>
> > The end result is exactly that
> >
> >   compute_driver=libvirt
> >
> > will work, along with backwards compat for the original name.
> >
> > It just needs to be resurrected and finished off.
>
> Indeed, it looks like that is definitely something to have as a
> priority item. Even if those patches were resurrected it looks
> like quite alot more work is needed, give that they only tackle
> 3 out of 44+ config parameters!
>
> Do we have any official position on config file upgrade support
> at this time ?  It would be helpful to reviewers if they could
> clearly identify whether a proposed config change is acceptable
> or not from an upgrade POV, since currently people are holding
> different changes to different standards before approval
>
> Daniel
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