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

[Martin Bjorklund <[e-mail]>]

Juergen Schoenwaelder <[e-mail]> wrote:
> 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.

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.


> 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.


/martin




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