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

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Mon, 12 November 2018 16:26 UTC

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Date: Mon, 12 Nov 2018 17:26:02 +0100
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: Martin Bjorklund <mbj@tail-f.com>
CC: <andy@yumaworks.com>, <netmod@ietf.org>
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Subject: Re: [netmod] New Version Notification for draft-verdt-netmod-yang-versioning-reqs-01.txt
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On Mon, Nov 12, 2018 at 05:21:55PM +0100, Martin Bjorklund wrote:
> Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> > On Fri, Nov 09, 2018 at 05:31:59PM +0100, Martin Bjorklund wrote:
> > > Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> > > > On Fri, Nov 09, 2018 at 02:37:29PM +0100, Martin Bjorklund wrote:
> > > > > 
> > > > > > 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.
> > > > >
> > > > 
> > > > Here is what 3.2 says:
> > > > 
> > > >        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.
> > > > 
> > > > This does _not_ say servers MUST implement this.
> > > > 
> > > > Item 3.2 establishes a requirement and for some solutions it may be
> > > > easy to satisfy this requirement, for others it may be more costly to
> > > > satisfy this requirement.
> > > > 
> > > > The whole requirements exercise becomes a rather pointless exercise if
> > > > we remove requirements so that certain solutions look more
> > > > attractive.
> > > 
> > > Ok, but that's not what I wrote.  I don't agree with this requirement
> > > which says that it MUST be possible for a server to support
> > > different revisions of a given module (again, if this is not the
> > > intention of the text, please clarify).  I simply don't think that
> > > this is a good requirement.
> > >
> > 
> > I can't follow you or I do not understand what you are after.
> > 
> >   In some versioning schemes, providing support for different
> >   'versions' is relatively easy. If I have modules foo-1 and foo-2,
> >   then I can implement foo-1 and foo-2 (or proper workable subsets of
> >   them) easily. And older clients expecting foo-1 may continue to work
> >   while newer clients move to foo-2. In other versioning schemes,
> >   providing the same possibility to migrate from foo version 1 to foo
> >   version 2, would lead to the support of foo in two different
> >   versions.
> 
> But module 'foo-2' is not a new revision of module 'foo-1'.  It might
> be that 'foo-2' represents a new version of the underlying "function"
> that 'foo-1' represents; but that is a different issue.

This depends on the versioning solution or what we consider a versioning
solution.

> > The requirement tries to express that it must be possible to have a
> > transition path where old clients can continue to function with the
> > old version while new clients start using the new version. The idea is
> > to state this as a requirement without making any assumptions about
> > the solutions.
> > 
> > Are you saying that a requirement saying that there should be a
> > possibility of a transition path is in general a bad requirement?
> 
> No (but I agree w/ Rob Wilton that it is unclear how this should be
> done in non-trivial examples), but again, that is not what I think 3.2
> says.  IMO 3.2 doesn't allow a solution that requires a new module for
> new NBC stuff, since it says that a client should be able to pick a
> particular revision of a module.
>

We apparently lack words for modules that may be versioned by new
module names.

/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/>