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

[Juergen Schoenwaelder <[e-mail]>]

On Fri, Nov 09, 2018 at 05:31:59PM +0100, Martin Bjorklund wrote:
> Juergen Schoenwaelder <[e-mail]> 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.

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?

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
Fax:   [phone]         <https://www.jacobs-university.de/>