Re: [netmod] initial comments on draft-rwilton-netmod-yang-packages

[Andy Bierman <[e-mail]>]

On Wed, Jan 30, 2019 at 7:16 AM Andy Bierman <[e-mail]> wrote:

>
>
> On Wed, Jan 30, 2019 at 4:19 AM Robert Wilton <[e-mail]> wrote:
>
>> Hi Andy,
>>
>> Thanks for the comments.
>> On 30/01/2019 01:22, Andy Bierman wrote:
>>
>> Hi,
>>
>> I originally brought up this issue in July 2015
>> https://datatracker.ietf.org/doc/draft-bierman-netmod-yang-package/
>>
>> Yes.
>>
>> The solution I propose is different in the sense that it uses YANG
>> instance data to define YANG packages rather than new YANG keywords.   I
>> believe that this should make it a lower cost solution to define and
>> implement.
>>
>>
>>
> I think yangvalidator.org has a better solution that does not change YANG
> conformance.
>
>

oops -- I meant yangcatalog.org

I don't agree that:

 (1) an instance document is easier for readers and writers.
It may be easier for tool makers, but that is subjective.
But the solution is irrelevant unless we agree on the problem first.

 (2) we need to specify YANG conformance for groups of modules

(3) it simplifies YANG to define conformance for modules and groups of
modules

(4) it is unclear how the packages are used by an operator

(5) the WG agreed on any problem to solve for which YANG packages is the
solution


Andy


> Andy
>
>
>>
>> I don't think the WG ever agreed on the problem that needs to be solved,
>> and that is still the case.
>>
>> That wasn't quite my impression.  I also think that folks were busy
>> focusing on other WG activity and didn't necessarily have the time to
>> concentrate on this.
>>
>> My draft was aiming on solving two broad problems:
>>
>>    The main goals of YANG package definitions include, but are not
>>    restricted to:
>>
>>    o  To act as a simplified YANG conformance mechanism.  Rather than
>>       conformance being performed against a set of individual YANG
>>       module revisions, conformance could also be more simply stated in
>>       terms of YANG packages, with a set modifications (e.g. additional
>>       modules, deviations, or features).
>>
>>    o  To allow YANG datastore schema to be specified in a more concise
>>       way rather than having to list all modules and revisions.  YANG
>>       package definitions can be defined in documents that can be
>>       referenced by a URL rather than requiring explicit lists of
>>       modules to be shared between client and server.  Hence, a YANG
>>       package must contain sufficient information to allow a client or
>>       server to precisely construct the schema associated with the
>>       package.
>>
>>
>>
>>
>>
>> In reality each server has 1 package -- its entire library.
>>
>> This doesn't apply to all servers.  For a long time, as a vendor, we have
>> had separate packages that can be independently installed, and which extend
>> the management model to cover the new functionality.  E.g. BNG
>> functionality could be in a separate, independently installable, package on
>> top of the base router functionality.
>>
>> For a Linux server, the manageability interface will depend on what
>> applications have been installed.
>>
>>
>> The SEMVER work shows
>> that vendors are treating platforms as independent release trains, and
>> not really
>> developing loadable packages.
>>
>> This depends on the vendor.  The YANG versioning work is trying to find a
>> solution that works across the industry.  I believe that the versioning
>> requirements are different for standards developed modules, vs industry
>> developed modules, vs vendor modules.
>>
>>
>>
>> I think YANG 1.2 improvements for conformance (e.g., YANG-redirects,
>> SEMVER import)
>> and  the YANG Catalog can solve the module compatibility issues. It is
>> more of a documentation
>> problem than a standards problem.
>>
>> Having a standard YANG module that can be used to define packages is
>> something this is useful and should be standardized.  I believe that this
>> is better than each vendor coming up with their own solution for this
>> problem.
>>
>> Thanks,
>> Rob
>>
>>
>>
>>
>> Andy
>>
>>
>>
>>
>> On Tue, Jan 29, 2019 at 4:55 PM Sterne, Jason (Nokia - CA/Ottawa) <
>> [e-mail]> wrote:
>>
>>> Thanks Rob. Please see inline.
>>>
>>> Jason
>>>
>>>
>>>
>>> *From:* Robert Wilton <[e-mail]>
>>> *Sent:* Thursday, January 24, 2019 1:16 PM
>>> *To:* Sterne, Jason (Nokia - CA/Ottawa) <[e-mail]>;
>>> [e-mail]
>>> *Subject:* Re: initial comments on draft-rwilton-netmod-yang-packages
>>>
>>>
>>>
>>> Hi Jason,
>>>
>>> Thanks for the review and comments.
>>>
>>> I've put some responses inline ...
>>>
>>> On 24/01/2019 14:56, Sterne, Jason (Nokia - CA/Ottawa) wrote:
>>>
>>> Hi guys,
>>>
>>>
>>>
>>> I've gotten most of the way through the draft and have some initial
>>> comments. I haven't digested the section 10 open issues yet or the examples.
>>>
>>>
>>>
>>> Section 5 mentions the following:
>>>
>>>    YANG library is augmented to allow servers to report the packages
>>>
>>>    that they implement and to associate those packages back to
>>>
>>>    particular datastore schema.
>>>
>>>
>>>
>>> Does the combination of this draft and rfc7895bis somehow allow the same
>>> package to be advertised in 2 different datastores, but with different
>>> deviations in each datastore? I'm thinking of a case, for example, where a
>>> package is fully supported in the running but the package minus a few
>>> modules (or parts of modules) is supported in the operational datastore.
>>> There seems to be a 1:1 relationship between package and rfc7895bis schema.
>>>
>>> So, the intention is no, not directly.
>>>
>>> My aim here is that <running> would implement package "foo", and
>>> <operational> would implement package "modified-foo".  Package
>>> "modified-foo" would import package "foo" and also specify the set of
>>> modules that contain the deviations "foo".
>>>
>>> I didn't want a server to be able to see that I implement package "foo",
>>> but then I have all these deviations that change its behavior.  Instead, it
>>> is really implementing a different package that is based on "foo".
>>>
>>>
>>>
>>>
>>>
>>> The packages draft doesn't include any specific leaf-list for
>>> deviations. Section 7.2 mentions that deviations could be expressed by
>>> including modules that happen to contain deviations. That seems a bit
>>> inconsistent with rfc7895bis that has a specific leaf-list of deviations
>>> (and NETCONF hello that specifically explicitly labels deviation modules).
>>>
>>> I'm conflicted on this one.  I don't really like the deviation list in
>>> YANG library because I regard it as a duplicate source of information, and
>>> then there is a question of which source of data do you trust.  E.g. do you
>>> process a deviation in a module that is not listed in the deviations module
>>> list?
>>>
>>> *[>>JTS: ] Good point. I suppose this issue applies today already. i.e.
>>> what if one of the modules advertised in the <hello> is a module of
>>> deviations (without having been referenced by another module as a deviation
>>> module).*
>>>
>>>
>>>
>>>
>>>
>>> Section 5.1 says the package must be referentially complete. I can see
>>> the advantages of that although wondering if that might limit flexibility
>>> of partitioning modules into packages. I could imagine use cases for
>>> dividing a large set of modules into a few packages that might rev
>>> independently but can still all work together (especially if they rev in a
>>> bc manner). But maybe that just starts to introduce too much complexity?
>>>
>>> Yes, having partial packages may be useful.  Perhaps just adding a leaf
>>> to indicate whether a package is referentially complete could be the answer
>>> here.
>>>
>>>
>>>
>>>
>>>
>>> I didn't understand this part of section 5.1. Can you maybe illustrate
>>> with an example?
>>>
>>>       The version/revision of a module listed in the package module list
>>>
>>>       supercedes any version/revision of the module listed in a imported
>>>
>>>       package module list.  This allows a package to resolve any
>>>
>>>       conflicting implemented module versions/revisions in imported
>>>
>>>       packages.
>>>
>>> Probably best to see example B.3. in the appendix because it exactly
>>> illustrates this point.
>>>
>>> Basically:
>>> 1) Packages must explicitly list all versions of all modules they
>>> define/import.
>>> 2) If two imported packages define different versions of modules, then
>>> the package that is importing them needs a way to define which version to
>>> use.
>>> 3) A package needs a way to override the version of module specified in
>>> an imported package.
>>>
>>> *[>>JTS: ] Thx. That example does help. I suppose the designer of the
>>> package needs to carefully check that the version they select can be
>>> successfully used by all the modules in the package. *
>>>
>>> *I think there is a minor typo in example B.3.  The example-3-pkg is
>>> importing "* *example-import-1" but I believe you meant "* *example-import-1-pkg"
>>> (and some for import-2).*
>>>
>>>
>>>
>>> It might be a good idea to add a parent-version to the package module
>>> (to allow tracking lineage of packages).
>>>
>>> Agreed, or maybe allowing a revision history like modules.  Not sure
>>> which is better here.  Packages could get a lot of updates, and a long
>>> revision history would not be helpful at all.
>>>
>>> *[>>JTS: ] I think a minimum of just specifying the direct parent is
>>> enough to build the full tree of lineage. We don't need a long history of N
>>> revisions.*
>>>
>>>
>>>
>>>
>>>
>>> I like the use of groupings. That allows a manager to use this as a
>>> building block to compose a model that has a list of packages.
>>>
>>> OK.
>>>
>>>
>>>
>>>
>>>
>>> Having a global list of mandatory features (vs having the mandatory
>>> feature a per-module list) means inventing the new <module-name>:<feature>
>>> format. Should we instead somehow put the mandatory features against each
>>> module of the package?
>>>
>>> Perhaps.  My thinking here was to have the list of features high up and
>>> very easy to find/parse.
>>>
>>>
>>>
>>>
>>>
>>> The location leaf is a uri but then the description says it must be a
>>> url (where the model can be retrieved). I do like that the namespace is
>>> separate from the location, but maybe we should make location a url type?
>>>
>>> Yes, I was thinking that is should be a URL.
>>>
>>>
>>>
>>>
>>>
>>> Do we need a namespace for package names in the model?
>>>
>>> I had them in an earlier version, but I took them out, because I wasn't
>>> sure that they are really useful/required.
>>>
>>> Defining a format to make package names themselves globally unique might
>>> be sufficient.
>>>
>>> *[>>JTS: ] I'm OK with that. It is similar to how we're finding that it
>>> is useful that YANG module names are globally unique (i.e. by naming with
>>> ietf-xxxx or companyabc-xxx).*
>>>
>>>
>>>
>>>
>>>
>>> In 7.3 we only reference module-sets and not modules. So the grouping of
>>> modules into sets and packages must be the same?
>>>
>>> Not necessarily.
>>>
>>> I am trying to reuse the module-set definitions as much as possible (to
>>> avoid duplication).  One issue here is that module-sets are combined then
>>> all the modules must not overlap, which doesn't make the mapping to
>>> module-sets quite so clean.
>>>
>>>
>>>
>>>
>>>
>>> A schema can only have a single package. I think that works but it means
>>> a server would advertise multiple schemas if it wants to support multiple
>>> packages. I'm not sure if there are some downsides to that (it just
>>> surprised me).
>>>
>>> My aim here was:
>>>  - multiple packages are advertised in yang-library/packages
>>>  - datastores only report that they "implement" one [top level] package
>>> version.  [The package itself might import other packages.]
>>>
>>> If we do package selection, then for a given YANG client session, and
>>> the version of YANG library available/reported by that session, it would
>>> appear as if the server only implements one top level package for a
>>> datastore.  Different clients choosing different versions would see
>>> slightly different output depending on which package version they had
>>> selected to use.
>>>
>>> Thanks again for the review and the comments!
>>>
>>> Rob
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Jason
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> *From:* netmod <[e-mail]> <[e-mail]> *On
>>> Behalf Of *Robert Wilton
>>> *Sent:* Thursday, December 20, 2018 12:45 PM
>>> *To:* [e-mail]
>>> *Subject:* [netmod] YANG Packages
>>>
>>>
>>>
>>> Hi,
>>>
>>> I've written up an ID for a potential solution for YANG packages using
>>> instance data:
>>>
>>> Abstract
>>>
>>>
>>>
>>>    This document defines YANG packages, an organizational structure
>>>
>>>    holding a set of related YANG modules, that can be used to simplify
>>>
>>>    the conformance and sharing of YANG schema.  It describes how YANG
>>>
>>>    instance data documents are used to define YANG packages, and how the
>>>
>>>    YANG library information published by a server can be augmented with
>>>
>>>    additional packaging related information.
>>>
>>> https://datatracker.ietf.org/doc/draft-rwilton-netmod-yang-packages/
>>>
>>> Potentially this work may be of use as part of the YANG versioning
>>> design team work.  In addition, if the WG likes this approach of defining
>>> YANG packages, then it might also be useful to bind a schema to a YANG
>>> instance data document.
>>>
>>> Some questions for members of the WG:
>>>
>>> 1) Do members of the WG agree that YANG packages is something that needs
>>> to be solved?
>>>
>>> 2) Is the approach in this draft of defining these as instance data
>>> documents a good starting point?
>>>
>>> 3) This approach augments YANG library-bis, reusing module-sets, but not
>>> replacing the way that modules are reported in YANG library-bis.  Is this
>>> the right approach?  This approach tries to allow module-sets to be reused
>>> for both schema and packages, but the YANG library-bis rules for combining
>>> module-sets (i.e. no conflicts) may make this harder to really reuse the
>>> module-sets for both purposes.
>>>
>>> Of course, any other comments or feedback is welcome and appreciated.
>>>
>>> Thanks,
>>> Rob
>>>
>>> _______________________________________________
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>>> https://www.ietf.org/mailman/listinfo/netmod
>>>
>>