Re: [netmod] New Version Notification for draft-verdt-netmod-yang-versioning-reqs-01.txt

Martin Bjorklund <mbj@tail-f.com> Fri, 09 November 2018 13:37 UTC

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Subject: Re: [netmod] New Version Notification for draft-verdt-netmod-yang-versioning-reqs-01.txt
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Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> On Thu, Nov 08, 2018 at 10:42:20PM +0100, Martin Bjorklund wrote:
> > Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> > > On Sat, Oct 27, 2018 at 06:50:58AM -0700, Andy Bierman wrote:
> > > > 
> > > > This is what we have today only if modules are updated in legal ways.
> > > > The 3.1 requirement says this backward compatibility is maintained even
> > > > if the module is updated in violation of the module update rules.
> > > >
> > > 
> > > It is stating a requirement. How solutions meet the requirement is for
> > > the solutions to figure out.
> > > 
> > > > How would 3.1 be met if the WG decided to just add a new 'datastore'
> > > > key leaf to the /modules-state/module list?
> > > 
> > > Depends on the solution I guess.
> > >  
> > > > IMO the current "deprecate and start over" is actually the easiest
> > > > and most robust solution path, and it requires no changes to YANG or
> > > > the protocols.
> > > 
> > > Yep. But there are people who think that other solutions can do
> > > better. The challenge is to find out whether they actually do better
> > > or for whom they do better (and if someone has to pay a price for it).
> > > For having this discussions, it is good to write down requirements.
> > > 
> > > > >        3.2  The solution MUST provide a mechanism to allow servers to
> > > > >             simultaneously support clients using different revisions of
> > > > >             modules.  A client's choice of particular revision of one or
> > > > >             more modules may restrict the particular revision of other
> > > > >             modules that may be used in the same request or session.
> > > > >
> > > > > Today, the version number is effectively an (implicit) part of the
> > > > > module name (plus the revision date for backwards compatible changes).
> > > > > Hence, my understanding is that today's model does satisfy 3.2 as
> > > > > well.
> > > > 
> > > > This is not what we have at all. RFC 7950 says a server can only implement
> > > > one revision of a module.
> > > >
> > > 
> > > A new version today essentially means a new module name and I do not
> > > see a conflict with what I wrote.
> > 
> > Then I think this requirement needs clarification.  It says "different
> > revision of modules", which can be interpreted as different revisions
> > of *the same* module.
> > 
> > Also the second part of the paragraph seems to indicate multiple
> > revisions of the same module in the server.
> > 
> > I do not agree with this requirement.
> 
> Today, you need to create a new module if you make NBC changes to
> existing changes (e.g., you change Bool to Int {0..1} and you are not
> creating a new leaf). Since there are now two modules, you _can_
> implement both modules if that makes sense.

Yes.

> If we allow to make such changes as part of a module revision, i.e.,
> without creating a new module, I think we should not loose the ability
> to implement both the old version and the new version.

I don't think we should allow such changes, and if we did, I don't
think that both revisions should be implemented at the same time.  I
think the overall solution would just be too complex.

> I think we need to distinguish between the agreement on the
> requirement, namely that a server should be able to provide support
> for an old and a new definition, and agreement on the solution.
> 
> Do you disagree with the requirement? Or do you disagree with the
> consequences of implementing multiple versions of the same module
> for some of the proposed new versioning schemes? Or both?

I do not agree with the requirement that a server MUST be able to
support multiple revisions of the same module, which is how I
interpret 3.2.  If this is not the intention of 3.2, maybe it can be
clarified.


/martin





> 
> /js
> 
> -- 
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
>