[netmod] Comments on draft-ietf-netmod-yang-module-versioning-09

[Andy Bierman <[e-mail]>]

Hi,

Most of the document focuses on the administrative details that will
be required to update a YANG module. (Lots of them).

My concern is with YANG 1.1 Co-existence and deployment of this new RFC.
(Sec 3.1)

https://datatracker.ietf.org/doc/html/draft-ietf-netmod-yang-module-versioning-09#section-3.1

A client (or another tool) that is compliant with RFC 7950 is
not required to be aware of the new YANG extensions, or expect
NBC changes in new module revisions.  It is not a good idea to
allow NBC changes in a YANG 1.1 module. IMO the new rules
need to apply to a new YANG language version.  It is not reasonable
to expect YANG 1.1 tools to work even if MUST requirements are removed.

Since YANG 1.1 Co-existence is not possible, vendors will decide
for themselves how much NBC they want in their implementations.
Breaking a YANG 1.1 client tool is still a problem they will have to deal
with.

This new RFC could encourage instability and poor engineering practices in
YANG APIs.
IMO best practice is still to introduce a new identifier and phase out
the old identifier with status=deprecated, then obsolete.
This is how opensource usually works (for good reason).


Andy