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

[Robert Wilton <[e-mail]>]

On 30/01/2019 17:31, Andy Bierman wrote:
>
>
> On Wed, Jan 30, 2019 at 8:02 AM Robert Wilton <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>
>     On 30/01/2019 15:16, Andy Bierman wrote:
>>
>>
>>     On Wed, Jan 30, 2019 at 4:19 AM Robert Wilton <[e-mail]
>>     <mailto:[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 <http://yangvalidator.org> has a better
>>     solution that does not change YANG conformance.
>
>     Do you mean that we can just use zip files with the list of modules?
>
>
> I don't care about the solution details yet. They are 2nd order problems.
>
> Conformance means "what modules are required to be implemented together".
> It is not clear that this problem can be solved.  The augment-stmt 
> defines implicit
> multi-module conformance.  I am not convinced that the extra work of 
> defining package conformance
> is worth it.

So, I'm not proposing backing any sort of package conformance into the 
language at all.  A package is just metadata that defines that a set of 
modules, at particular revisions/versions, work together and can 
represent part of a YANG schema.

This is equivalent to
  - how a zip file of YANG modules provided to yangvalidator would work.
  - getting the contents of YANG library from a server (but a YANG 
packages soln can also work offline)
  - fetching the modules from YANG catalog (if they have been labelled 
appropriately), although I'm not convinced that this universally works 
today.

But in terms of the usability of YANG, I don't think that doing 
conformance only at the module level is really sufficient. Clients need 
to be coding against sets of modules at particular versions that are 
known to work together, and known that multiple server vendors will 
implement.

A pick and mix appropriate to module revisions doesn't seem to help anyone.


>
> The issue of what modules does vendor A implement is not a conformance 
> problem.
> It is just more metadata and YANG Catalog is focused on providing that 
> data.

Does YANG catalog indicate the set of IETF modules that I would need to 
implement L2VPN services on a device?

Module tags could be used to do this (another packaging solution), but 
this would cause a proliferation of tags when it comes to versioning, 
since I don't think that you can cleanly bake semver into module tags.


>
>     I don't really see how this helps.
>
>     Consider:
>     - server vendor A, implements some subset of the OpenConfig YANG
>     modules, each at a particular version, along with some deviations
>     and vendor augmentations.
>     - server vendor B, implements the same subset of the OpenConfig
>     YANG modules, but at different versions, along with some
>     deviations and vendor augmentations.
>     - server vendor C, implements a slightly different set of the
>     OpenConfig YANG modules, but at different versions, along with
>     some deviations and vendor augmentations.
>
>     As a client, how do I know what module versions to code against,
>     when I want to work with devices provided by all three vendors?
>
>
>
> The vendors publish their implementation details on yangcatalog and 
> you get the info
> and see what modules are in common.
>
> There are only market requirements determining what group of modules 
> has to exist
> in an implementation.  It is not clear to me that formalizing these 
> requirements
> is something the industry will do effectively.  Module tags already 
> provide a way
> to conceptually group modules together.
>
> Seems like every vendor has openconfig, foo-openconfig, and 
> foo-openconfig-deviations
> so that there are no agreed upon subsets. Even if openconfig had 
> properly documented
> subsets, would your client even be able to code to it (ignoring 
> add-ons and deviations).

I think that answer will converge on yes, I don't know how long it will 
take.  It would probably be better if at the time that protocol 
specifications are written, that the authors of the specifications also 
write the YANG modules to manage them at the same time.

>
>     I might be wrong, but I think that the OC solution is use git
>     tags, so they tag sets of modules that are expected to work
>     together and also to provide a linear release history of their
>     sets of modules.  So, if everyone implements the module versions
>     associated with a git tag then it should convert a two dimensional
>     problem of module revisions into a linear problem.  The YANG
>     packages draft is aiming to provide a solution to this problem
>     that doesn't require the use of git, or sending zip files of
>     modules around.
>
>
>     At the moment, it seems that everyone is doing this in different ways:
>      - Yumawork customers/servers use zip files of modules for
>     conformance.
>
>
> Not sure what this means.
> Actually the server libraries can be loaded and unloaded.
> Module can be standalone libraries or grouped as bundles.
> But this seems like an implementation detail, unrelated to conformance.
>
>
>      - OpenConfig client/server implementations use git tags, or git
>     refpoints.
>      - Cisco customers use the contents of directories on github
>     YangModels.
>
>     Finally, this draft doesn't change YANG conformance, it just
>     expresses it in what is intended to be a simpler way.
>
>
> It adds another conformance system to maintain.
> The language only recognizes module to module interfaces, not package 
> to package.

I propose that at the language level conformance is at the module level 
(modulo import-by-version).


> That adds more complexity. It doesn't take away any complexity.

It is meant to be a simpler way of packaging up, and trying to control 
and manage the complexity that already exists today.

E.g. I could give a YANG compiler the name, version, and location of a 
package and tell it to build the entire schema associated with that 
package.

In a somewhat similar way, when I write code, my build file specifies 
which libraries I depend on, and their versions, but I can leave it to 
the build tool to determine what those libraries themselves depend on 
and recursively pull in all the dependencies.


>
> If there was a standard to load and unload modular functionality at 
> boot-time or run-time,
> then I could see why there is a need to have a standard to define YANG 
> packages.

I agree that this is another example of where they could be useful.

Thanks,
Rob


>
>     Thanks,
>     Rob
>
>
>
> 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]
>>>         <mailto:[e-mail]>> wrote:
>>>
>>>             Thanks Rob. Please see inline.
>>>
>>>             Jason
>>>
>>>             *From:*Robert Wilton <[e-mail]
>>>             <mailto:[e-mail]>>
>>>             *Sent:* Thursday, January 24, 2019 1:16 PM
>>>             *To:* Sterne, Jason (Nokia - CA/Ottawa)
>>>             <[e-mail]
>>>             <mailto:[e-mail]>>; [e-mail]
>>>             <mailto:[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]>
>>>                 <mailto:[e-mail]> *On Behalf Of
>>>                 *Robert Wilton
>>>                 *Sent:* Thursday, December 20, 2018 12:45 PM
>>>                 *To:* [e-mail] <mailto:[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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>>>