Re: [Netconf] YANG Doctor question: empty mandatory choice?

Andy Bierman <andy@yumaworks.com> Thu, 02 August 2018 15:25 UTC

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From: Andy Bierman <andy@yumaworks.com>
Date: Thu, 2 Aug 2018 08:25:14 -0700
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To: Kent Watsen <kwatsen@juniper.net>
Cc: Alexander Clemm <alexander.clemm@huawei.com>, Martin Bjorklund <mbj@tail-f.com>, "evoit=40cisco.com@dmarc.ietf.org" <evoit=40cisco.com@dmarc.ietf.org>, "netconf@ietf.org" <netconf@ietf.org>
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Subject: Re: [Netconf] YANG Doctor question: empty mandatory choice?
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On Thu, Aug 2, 2018 at 8:11 AM, Kent Watsen <kwatsen@juniper.net> wrote:

>
> I am sympathetic to Eric's and Einar's observation that a given
> subscription, having multiple receivers, is likely to have all the
> receivers using the same transport and encoding.
>
> The thought behind this is that, assuming there are multiple distinct
> applications, each application will selfishly create its own subscription;
> it will not try to see if there is another existing subscription that
> matches its needs.
>
> Thus, in effect, the *only* purpose for there being a *list* of receivers
> is for enabling high availability, which I think is okay.  I wish the text
> was clearer about this objective.
>
> What I object to is the way that this restriction is currently implemented
> using identities, which requires the "notif" models to do something right.
> Better would be a "must" expression that says the count of the descendants
> is exactly one.  Can you do that?
>


Is there a way to make multiple receivers per subscription
optional-to-implement
(another YANG feature?)

Anyone implementing configured subscriptions is forced to support multiple
receivers.
Does that mean it is harmful to the Internet if only 1 receiver per
subscription is allowed?

I was told this feature is required because it is too much of a burden on
the client to
create a separate subscription for each receiver.  IMO this is nonsense,
but I won't
implement configured subscriptions anyway.



> Kent // contributor
>
>

Andy


> ===== original message =====
>
> I am wondering why we are reopening the issue of multiple
> encodings/transports per receiver vs per subscription?
>
> Having single transport / encoding per subscription is a simpler design
> (feedback from implementors; simplifies dealing with any error conditions
> due to encoding that would affect one receiver but not others in the same
> subscription; Einar has explained this in the past) and, while I am in
> general a fan of general design, there does not seem to be business
> requirements and scenarios that demand this - and even if there were, this
> would constitute merely an optimization (since if you have different
> receivers who want different encodings/tranport, you can always simply
> create another subscription).
>
> If in the future there is really desire to add this as an additional
> feature, we can put this into a -bis version.  (Adding stuff will be easier
> than taking things away.)  Let's just be done.
>
> --- Alex
>
> > -----Original Message-----
> > From: Netconf [mailto:netconf-bounces@ietf.org] On Behalf Of Martin
> > Bjorklund
> > Sent: Tuesday, July 31, 2018 7:51 AM
> > To: kwatsen@juniper.net
> > Cc: evoit=40cisco.com@dmarc.ietf.org; netconf@ietf.org
> > Subject: Re: [Netconf] YANG Doctor question: empty mandatory choice?
> >
> > Kent Watsen <kwatsen@juniper.net> wrote:
> > > [removing yang-doctors list, and updating subject line accordingly]
> > >
> > >
> > > >> > Why do all receivers of a subscription have to use the same
> > transport?
> > > >>
> > > >> This was something that Martin and Eric worked out before we did
> > > >> the first Last Call.  Eric doesn't seem to know the particular
> > > >> reason, other than Martin seems to think it’s easier.
> > > >
> > > > No; I personally also prefer a design where each receiver has its
> > > > own transport + encoding.
> > >
> > > +1
> > >
> > >
> > > > The original model had a common "encoding" for all receivers, and
> > > > then a receiver-specific transport - I think this is even worse,
> > >
> > > Agreed.
> > >
> > >
> > > > and suggested to have transport + encoding defined together
> > > > preferrably receiver-specifc or else common for all receivers.
> > > >
> > > > If the WG now believes that the transport + encoding should be done
> > > > per receiver, this should be fairly easy to change.
> > >
> > > I also prefer per receiver, and I think that doing so will simplify
> > > the model, as neither the mandatory "transport" nor the [not
> > > mandatory?] "encoding" leaves have to be specified.
> > >
> > > In particular, my thoughts are that the "notif" model should provide
> > > for the encoding selection, if needed (it's not needed for NETCONF, or
> > > COAP I imagine).
> >
> > I agree.  I think this would be a cleaner design.
> >
> >
> > /martin
> >
> >
> > >
> > > In the case of RESTCONF, we could update the ietf-restconf-client and
> > > ietf-restconf-server models to include an "encodings" leaf-list, to
> > > configure the RESTCONF server which encodings it should support.  We
> > > likely need to do something similar to configure which HTTP versions
> > > should be supported.  Now, in a general RC server, the server could
> > > support both but, if the restconf-notif draft has its own list of
> > > restconf-servers (i.e., it uses the "restconf-server-grouping" itself,
> > > see my July 19 email for a YANG example), then a constraint could be
> > > added limiting the number "supported" to just one.  Thus, when the RC
> > > server reboots, and connects to the receiver and *automatically* (no
> > > client RPC) starts pushing notifications, it can know what encoding to
> > > use.
> > >
> > > I'm still unsure if its legal for an RC server to automatically push
> > > notifications without a client-initiated RPC of any sort, and I'm also
> > > uncertain if supporting *configured* subscriptions for NC or RC is
> > > needed (see my message July 20 email).  So, some of this may work
> > > itself out as we progress.
> > >
> > > I know that we're not defining the *configured* notif drafts in this
> > > first effort, the we are publishing the SN draft with a configuration
> > > model, my only concern now is configuration model presented in the SN
> > > draft.
> > >
> > >
> > > Kent // contributor
> > >
> > >
> > _______________________________________________
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