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

Martin Bjorklund <mbj@tail-f.com> Sun, 05 August 2018 09:21 UTC

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Date: Sun, 05 Aug 2018 11:21:50 +0200 (CEST)
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Subject: Re: [Netconf] YANG Doctor question: empty mandatory choice?
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Andy Bierman <andy@yumaworks.com> wrote:
> On Thu, Aug 2, 2018 at 9:04 AM, Einar Nilsen-Nygaard (einarnn) <
> einarnn=40cisco.com@dmarc.ietf.org> wrote:
> 
> > Inline...
> >
> > On 2 Aug 2018, at 16:11, 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.
> >
> >
> > einarnn> Absolutely. I see very few real world cases where it is likely
> > that we will see same subscription with different receivers using different
> > encodings. It is a step too far IMO.
> >
> > 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.
> >
> >
> > einarnn> This is the likely outcome if you are in a multi-manager scenario
> > anyway. We shouldn’t be trying to optimise anything related to thinking
> > that *distinct* consumers will try to reuse others’ subscriptions in a
> > spirit of good citizenship. It just won’t, pragmatically, happen. What
> > would be way more likely to happen to support this is that the distribution
> > out to multiple distinct consumers will happen by way of middleware put in
> > place by the customer.
> >
> > 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.
> >
> >
> > einarnn> Agreed. Let’s just move past this issue
> >
> >
> 
> OK, I do not want to hold up dynamic subscriptions.
> I do not agree with the design practice of empty mandatory choice.
> It looks like a band-aid for a broken development process, not good
> architecture.
> 
> Is it really such a complex problem to define a case with an address/port
> end-point?
> Sorry I missed the rationale for why removing such an obvious data model
> for an endpoint
> so it can be replaced with proprietary augments instead.  What are vendors
> using to model
> an endpoint that is so different from host/port?

For NETCONF, you would have a leafref to a call-home endpoint, as
defined in the ietf-netconf-server model.  In addition to the address
/ port, it has certificates and keys.



/martin


> 
> 
> Cheers,
> >
> > Einar
> >
> 
> Andy
> 
> 
> >
> >
> > 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?
> >
> > Kent // contributor
> >
> >
> > ===== 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 <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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