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

"Reshad Rahman (rrahman)" <rrahman@cisco.com> Fri, 09 November 2018 13:46 UTC

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From: "Reshad Rahman (rrahman)" <rrahman@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>, "j.schoenwaelder@jacobs-university.de" <j.schoenwaelder@jacobs-university.de>
CC: "netmod@ietf.org" <netmod@ietf.org>
Thread-Topic: [netmod] New Version Notification for draft-verdt-netmod-yang-versioning-reqs-01.txt
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Date: Fri, 9 Nov 2018 13:46:08 +0000
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References: <20181027211355.ppu7wavjcq2butc4@anna.jacobs.jacobs-university.de> <20181108.224220.1513800936571555652.mbj@tail-f.com> <20181109081557.kzalxvnsk2k2fycm@anna.jacobs.jacobs-university.de> <20181109.143729.1869485019013831956.mbj@tail-f.com>
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Subject: Re: [netmod] New Version Notification for draft-verdt-netmod-yang-versioning-reqs-01.txt
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On 2018-11-09, 8:37 PM, "netmod on behalf of Martin Bjorklund" <netmod-bounces@ietf.org on behalf of mbj@tail-f.com> wrote:

    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.
    
<RR> It says "The solution MUST provide...", so the solution draft MUST provide a solution on how to do this. Whether a server implements the solution or not is a different matter. We realize this is a pain for most servers but some servers may be able to do it.

Regards,
Reshad.
    
    /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/>
    > 
    
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