Re: [Netconf] nmda-restconf operations (was: netconf-binary-encoding comments)

[Andy Bierman <[e-mail]>]

On Wed, Jul 11, 2018 at 10:16 AM, Ladislav Lhotka <[e-mail]> wrote:

> On Wed, 2018-07-11 at 08:40 -0700, Andy Bierman wrote:
> >
> >
> > On Wed, Jul 11, 2018 at 4:22 AM, Ladislav Lhotka <[e-mail]> wrote:
> > > Kent Watsen <[e-mail]> writes:
> > >
> > > >>> This isn't what I meant.  To be more specific, I'm wondering if the
> > > nmda-restconf
> > > >>> draft would benefit from having a sentence like:
> > > >>>
> > > >>>    A RESTCONF server supporting NMDA datastores MAY implement the
> > > >>>    "ietf-netconf" [RFC6241] and "ietf-netconf-nmda" [I-D.
> ietf-netconf-
> > > nmda-
> > > >>>    netconf] modules to enable the NETCONF operations defined in
> those
> > > >>>    drafts to appear {+restconf}/operations resource.
> > > >>>
> > > >>> Note: I put "MAY" as RESTCONF may someday have a more native way
> to do
> > > this.
> > > >>>
> > > >>
> > > >> Well, "ietf-netconf" does not really support NMDA well and this is
> why
> > > >> we have "ietf-netconf-nmda". Does not make much sense to point to
> > > >> "ietf-netconf" in an NMDA document.
> > > >
> > > > But we'd still need lock, unlock, commit, commit-confirmed, etc.,
> > > > right?
> > >
> > > These would make RESTCONF server stateful, thus violating REST
> principles.
> > > My
> > > draft
> > >
> > > https://datatracker.ietf.org/doc/draft-lhotka-netconf-
> restconf-transactions/
> > >
> > > tries to achieve similar effects in a RESTful way.
> > >
> >
> >
> > I like the idea of "private candidate" datastores you call "staging".
> > I would keep the term candidate.
>
> The problem with this is that <candidate> in NETCONF has a looser
> semantics (it
> can also be shared).
>
> >
> > This idea was discussed during RESTCONF draft development, but
> > as the client creating a "transaction" resource. I think your draft is on
> > the right track, and datastores are protocol-independent so NETCONF
> > can use the same datastores with RPC operations.
>
> Yes, it can certainly be improved. I already have some pending updates,
> but I
> wanted to keep it simple for start.
>
> >
> > You ignore the problem of concurrent edits, which is why this idea was
> not
> > pursued
> > at the time. What happens when the altered data overlaps across private
> > candidates?
>
> I don't ignore it, the text says that the user's staging datastore has to
> be
> atomically merged into <intended>, I just didn't want to specify the
> procedure.
> In any case, the result has to be a valid <intended>. But I am open to a
> discussion.
>


Leaving it as an implementation detail is the IETF's way of ignoring
problems.


>
> > What are the procedures equivalent to git pull, push, merge?
> > How are collisions handled? What exactly is a collision?
> > Not trivial standards issues to solve.
>
> I think it can be left open, I even suspect there is no universal solution
> suitable for all use cases. Our implementation (JetConf) does the
> following:
>
> - each user's edit operation is applied to the staging datastore and also
> recorded in a journal
>
> - at commit, if <intended> hasn't been changed in the mean time, then the
> staging datastore simply becomes <intended>
>
> - otherwise, the edit operations from the journal are applied sequentially
> on
> the actual contents of <intended>.
>
>

This is "last one wins".
You will find this sort of works for create and merge but no so much for
replace and delete.



> (Actually, we are not NMDA-compatible yet and don't have <intended> but it
> works
> this way).
>
> Lada
>


Andy


>
> >
> > > Lada
> > >
> >
> >
> > Andy
> >
> > > >
> > > > Maybe it's a moot point, since ietf-netconf-nmda requires that ietf-
> > > netconf
> > > > is implemented too, but I thought being explicit would be helpful
> here.
> > > >
> > > > So, adding something like this to nmda-restconf would be good?
> > > >
> > > >
> > > > Kent // contributor
> > > >
> > > > _______________________________________________
> > > > Netconf mailing list
> > > > [e-mail]
> > > > https://www.ietf.org/mailman/listinfo/netconf
> > >
> --
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
>