Hi, But the two drafts go way beyond fixing the problem your three examples illustrate. If the goal is to indicate that non-backwards compatible changes have occured, a single new extension statement could solve that. (As I probably have stated before, personally I don't think this is necessary).
Apart from the updates to RFC 7950 section 11, I am mostly concerned about the additional complexity the "pluggable" revision-label scheme brings. /martin "Rob Wilton \(rwilton\)" <rwilton=40cisco....@dmarc.ietf.org> wrote: > I'm wondering whether we are in the realm of missing the bigger > picture here, or perfection being the enemy of good enough. > > My first example: > > The sedate WG (https://datatracker.ietf.org/wg/sedate/about/) has > recently been rechartered to respecify the meaning of the date string > in a non-backwards compatible way. Yes, this same date string format > that is very widely implemented and deployed. I originally had a > block on the new charter until it was pointed out that the IETF > specification was being updated because it was inconsistent with the > ISO time specification and inconsistent with how the date string was > actually being used by implementations. I.e., the specification is > being updated to reflect reality. I.e., fixing the specification in a > non-backwards compatible way ends up being pragmatically the right > thing to do (and this is entirely allowed by the IETF process). > > Ideally, the date-and-time typedef in YANG would also be updated to > match the update to the definition in RFC 3339 by SEDATE. But this is > clearly not compliant with section 11 of RFC 7950 (because the value > space of allowed values is being narrowed). The only available choice > would be to define a new date-and-time-2 typedef which modules could > then update to. Of course, you cannot update the existing leaves to > use the new date-and-time-2 typedef because that also violates section > 11. So, you end up with two datetime leaves everywhere the > date-and-time typedef is used, hopefully with one deprecated (and at > some point, obsoleted). Of course, defining the new datetime version > leaves could also break any loosely related modules that may have > xpath expressions dependent on that date-time leaf (that the updating > module author may not even know about) which would need to be updated > to depend on either of the leaves. I also don't think that RFC 7950 > is clear about whether deprecated leaves must be implemented by all > implementations or not, so realistically clients will need to handle > setting either (or perhaps in some cases, both) of the datetime > leaves, depending on implementation, probably with a different mix > across modules (in vast stages of being updated). What happens if > some instances of those datetime leaves are mandatory configuration > and become obsolete? Is a client required to set it or not, the > pragmatic answer being that again RFC 7950 is unclear and again this > will likely be implementation dependent. What about if some of those > datetime leaves are list keys? I believe that the only solution that > RFC 7950 allows for would be to duplicate the list, deprecating the > old one, again requiring updates to all augmenting modules, and > corresponding impact and churn on clients and servers. > > I suspect that OpenConfig may also have a date-and-time typedef. I > can be certain about how they would handle this same issue - they will > just update the definition. Some clients/servers may have minor > impacts when they update to a new version of the model, but the impact > and effort required is minimal, and I think several orders of > magnitude less then the potential resultant churn than would happen by > strictly following the RFC 7950 section 11 rules. > > Some may argue that I'm not being pragmatic, and that this could just > be handled as a bugfix, changing the existing type. This is one of > the key things that the YANG versioning is trying to accomplish and > allow. It isn't aiming to say that module designers have carte blanch > to change modules in non-backwards compatible ways. Instead, it is > saying that in some cases, the pragmatic solution is to knowingly > break the RFC 7950 rules and make a breaking change because that > causes less impact. Further, a key aim of the versioning work is that > it is much better to be explicit that a breaking change has occurred > such that a client can easily be warned of that change and take any > mitigation necessary - which in the datetime instance above, is quite > possibly that no mitigation is required at all. > > Finally, I will note that rfc-6691-bis contains a change to the > datetime definition that is not backwards compatible with the existing > definition because the semantics of the leaf are being redefined. > > > A somewhat similar second example: > > The YANGs IP address type handling of zone information is very similar > to my first issue, where OpenConfig came to the pragmatic conclusion > that (in their models) 100% of the use cases of IP addresses only use > the numeric form without zone identifiers, and hence when someone sees > the typedef ip_address, this is what they are thinking of, so they > just pragmatically updated their definition of ip_address type. > > Somewhat related to this, I will note that rfc-6691-bis contains a > change to the ipv4-address and ipv6-address regex definition that is > not backwards compatible with the existing definition (it narrows the > valuespace for zone-ids restricting it to ASCII letters and digits > whereas previously it allowed for any language letters or digit > characters). I believe that this change is not strictly compatible > with RFC 7950 section 11, but I still think that this is the > pragmatically right change to make without introducing a new set of IP > address types, despite the fact that it could hypothetically break > some clients/servers, and we have no way of knowing in advance if that > will happen. > > > A third consideration: > > Yesterday, Jeff and Mahesh presented in a NETMOD interim on their > learnings from trying to write the IETF BGP model. One of their > outcomes is that they think that some of the other models recently > standardized by the IETF don’t interoperate well with the BGP model > and will need to be revised. I've no idea whether those changes can > all be made cleanly in a backwards compatible way, but I suspect not. > Hence, my concern here is that the IETF doesn't really have a great > path to getting a viable set of YANG models that work together, > because just publishing modules working in isolation doesn't solve the > industry problems. > > Because lots of the IETF YANG models have been written without a lot > of implementation experience (chicken and egg problem), often my > people who know the protocols but are not experts on YANG, means that > we can be sure that there are likely to be many bugs and flaws in the > YANG module RFCs that will need to be fixed or improved. I would > expect that some of these cannot be pragmatically fixed in a backwards > compatible way. > > --- > > My interpretation of the recent last call review comments is the > suggestion that we pivot to find a fundamentally different solution or > approach to solving this problem as an RFC7950bis. I believe that > would be a mistake. > > In summary, a group of participants have been diligently working on > this problem space for 5+ years. > > We have had a design team working on this area, and that solution was > then adopted by the WG. The authors and interested individuals > working on this area has presented updated drafts and updates to the > work at every IETF meeting for the last, 4+ years. Feedback at the > various stages/reviews/etc has always been considered, the authors > meetings have always been open, and I don't believe that the solution > drafts being taken to WG LC are architecturally significantly > different from the direction agreed during WG adoption of the > documents, although I do think that the documents are much improved > based on the feedback received. > > I also appreciate that Juergen has always publicly stated that this > work should be done as an update to the YANG language, but my > recollection was that he was in the rough on this issue, i.e., during > WG adoption, and since, at least until this IETF WG LC review. > > Hence, my concern, as an AD, is that if, after 5 years, the WG now > wants to take a fundamentally different path to standardizing this > work then I have concerns that the NETMOD WG isn't really functioning > properly and cohesively as a WG, and I'm very concerned that we won't > find any viable way forward for this work. I doubt that it will be > possible to get any quick consensus by opening up RFC 7950. We may > also find that the individuals who have invested a significant amount > of time and effort on this work don't have the desire or energy to > start from scratch again, when they have a solution that is good > enough for their needs. > > If I understand correctly, the fundamental objection to the module > versioning draft is around the updates to section 11 of RFC 7950, > which effectively state that changes MUST be backwards compatible, > whereas this draft states SHOULD be backwards compatible, without a > change to the YANG version number. Is that correct? > > If the existing deployment and evolution of YANG modules among > vendors, OpenConfig, IETF, and other SDOs strictly followed the rules > in RFC 7950 then I would probably agree that an update from YANG 1.1 > to YANG 1.2 is needed. But I think that the reality is that tools > must handle non-backwards compatible changes frequently happening in > YANG 1.0 (OpenConfig) and YANG 1.1 YANG modules anyway. I.e., I don't > believe that the "YANG 1.1 no breaking change contract" is being > widely honoured anyway, and instead is being treated as a goal or > aspiration. What these documents attempt to do is to move YANG module > evolution from what we currently have now where clients don't have any > way of really knowing how a module has evolved and whether they are > impacted to one that they do, and as part of that process they are > aiming to update the YANG versioning rules to better reflect how is it > being deployed and used. > > Hence, as am author, I still of the opinion that the best pragmatic > path forward is to try and get these documents to a shape where they > achieve rough consensus and are acceptable to the WG to be published > now, in the short term, as a good enough solution. After that point, > then I think that it would be great for some folks to form an idea on > a what YANG 1.2/2.0 could look like, but I think that coupling these > goals together would be a mistake. > > Regards, > Rob > > // Who doesn't really know which hat he is wearing for this comment, > but is only trying to do the right thing for the wider industry ... > > > > -----Original Message----- > > From: netmod <netmod-boun...@ietf.org> On Behalf Of Jürgen Schönwälder > > Sent: 06 June 2023 06:07 > > To: Martin Björklund <mbj+i...@4668.se> > > Cc: netmod@ietf.org > > Subject: Re: [netmod] Joint WGLC on "semver" and "module-versioning" > > drafts > > > > On Mon, Jun 05, 2023 at 10:32:51PM +0200, Martin Björklund wrote: > > > > > > > > If the goal is to produce YANG 1.2 which (i) integrates semantic > > > > versioning into YANG and (ii) fixes known bugs in YANG 1.1 and (iii) > > > > does not add any other new features, then having agreement on such a > > > > statement will help to steer the process. > > > > > > I hope that (i) doesn't happen. I think it is the proposed changes in > > > draft-ietf-netmod-yang-module-versioning that require a new YANG > > > version. If this new YANG version allows for other versioning schemes > > > than revision-date, then we can keep the modified semver scheme > > > outside the core document. > > > > > > > I consider the module update rules a part of a versioning model. The > > current update rules were written to support the current versioning > > model. If we want to support multiple versioning models, then we have > > to refactor the update rules out of the YANG language specification > > into separate versioning specifications, i.e., traditional YANG > > versioning and the new semver versioning. There are some language > > mechanisms (like the import statement), that have to be flexible > > enough to support multiple versioning schemes. > > > > Is it worth factoring the versioning model out of the language? I > > guess the opinions vary widely on this, depending on the dynamics of > > the software environment people are working in. > > > > /js > > > > -- > > Jürgen Schönwälder Constructor University Bremen gGmbH > > Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany > > Fax: +49 421 200 3103 <https://constructor.university/> > > > > _______________________________________________ > > netmod mailing list > > netmod@ietf.org > > https://www.ietf.org/mailman/listinfo/netmod > _______________________________________________ > netmod mailing list > netmod@ietf.org > https://www.ietf.org/mailman/listinfo/netmod _______________________________________________ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod
