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