Re: [Netconf] [netmod] magic leaf 'type' in IETF interfaces

On Wed, Dec 19, 2018 at 6:16 AM Ladislav Lhotka <lhotka@nic.cz> wrote:

> Jan Lindblad <janl@tail-f.com> writes:
>
> > Hi,
> >>> While I agree with Martin, in our systems we have a number of places,
> where the system does create configuration in running, due to
> >>>
> >>> different levels of automation and autonomous algorithms kick-in
> >>> the created config needs to be possible to be further modified by the
> operator
> >>> the created config needs to be referenced from operator created config
> >>> the created config is not always ephemeral, it might need to be part
> of backup/restore
> >> This is only a sampling from "the list of excuses". I have heard many
> more. The road to hell is paved with good intentions, however. If we want
> to build automation based on sound theory, clearly separating the orders
> from managers from a system's own operational view is key, IMO.
> Reliability, security, accountability are growing in importance, and they
> all play in this direction.
> >>
> >> We may not need to standardize rules to outlaw the above; the market
> will take care of that. What we need to ensure is that it is possible to be
> standards compliant without having to implement design excuses like these.
> >>
> >>
> >> NMDA has a lot of room for proprietary mechanisms for converting
> <running> to <intended>.
> >> Many times the features desired by engineers exceed the capabilities of
> YANG, such as
> >> a dynamic default leaf.  YANG allows a simple constant, and no business
> logic to pick the default.
> >> This is a very valid use of "server auto-magic".
> >>
> >> Maybe a future version of YANG can improve the client visibility into
> this "auto-magic"
> >
> > As you say, this is not uncommon. I usually recommend to leave out any
> > default statement, and write in the description what happens if this
> > leaf isn't set. The operator can then override the default by giving a
> > value.
>
> Anyway, this is not a case where the server writes something on its own
> to a configuration datastore.
>

I don't think it is a problem if NMDA or non-NMDA servers write to
<running>.
Just part of the complexity that is baked in -- NMDA does nothing to help
the client know
why <running> is different than <intended> anyway.

>
> >
> > While some more advanced features for default values may be of some
> > utility, the simplicity of YANG is also important. We don't want to
> > make the YANG models -- the interface contracts -- the new place for
> > all business logic.
>
> Absolutely.
>
>
I am not proposing YANG needs a new default-stmt. There is a
description-stmt
and vendors can add their own extensions to flag auto-magic data nodes.

> Lada
>
> >
> > /jan
>

Andy

> >
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> --
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
>