Re: [Netconf] comments on draft-ietf-netconf-subscribed-notifications-12

"Eric Voit (evoit)" <evoit@cisco.com> Thu, 14 June 2018 20:11 UTC

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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>, "alexander.clemm@huawei.com" <alexander.clemm@huawei.com>, "alex@clemm.org" <alex@clemm.org>
CC: "j.schoenwaelder@jacobs-university.de" <j.schoenwaelder@jacobs-university.de>, "netconf@ietf.org" <netconf@ietf.org>
Thread-Topic: [Netconf] comments on draft-ietf-netconf-subscribed-notifications-12
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Date: Thu, 14 Jun 2018 20:11:38 +0000
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Subject: Re: [Netconf] comments on draft-ietf-netconf-subscribed-notifications-12
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> From: Martin Bjorklund, June 14, 2018 2:40 PM
> 
> "Eric Voit (evoit)" <evoit@cisco.com> wrote:
> > > From: Martin Bjorklund, June 14, 2018 4:22 AM
> > >
> > > Hi,
> > >
> > > Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> > > > On Wed, Jun 13, 2018 at 03:36:01PM +0000, Eric Voit (evoit) wrote:
> > > > > Each of the terms used are different.  While they all are
> > > > > defined in the first
> > > document they are used, let me paraphrase the meanings of the
> > > definitions...
> > > > >
> > > > > Event - something that happened
> > > > >
> > > > > Event record - the recorded details of a single event
> > > > >
> > > > > Update record - one or more datastore node updates
> > > > >
> > > > > <notification> - a structure defined in RFC5277 which is as a
> > > > > wrapper which
> > > contains an event record.  A <notification> can exist without any
> > > active subscription.
> > > > >
> > > > > "notification" statement - a structure defined in RFC-7950
> > > > > section
> > > > > 7.16
> > > which allows the definition of event record types specific to a YANG
> > > module.
> > > The results of the a YANG "notification" statement are encoded in a
> > > <notification>.
> > > >
> > > > Here is where I am getting lost. The RFC 7950 notification
> > > > statement (its not a structure btw) does define the content of a
> notification.
> > > > And notification used to be defined in RFC 6241 as a
> > > > "server-initiated message indicating that a certain event has been
> > > > recognized by the server." Your notion of an event record may come
> > > > from the RFC 5277 format that adds an eventTime etc. but the
> > > > relationship of what is a YANG defined notification and how it
> > > > related to your event record and the <notification> structure is still
> unclear.
> > >
> > > I don't think we should align terminology with 5277.  More important
> > > is to align with the current set of documents; 7950 and 6241.
> >
> > Exactly.
> >
> > Note that there was no terms imported from 5277.
> > Subscribed-notifications does define an umbrella term "notification
> > message", and uses Section 2.6 to make the minimal connection
> > necessary to show that an RFC-5277 <notification> is a valid
> > "notification message".  BTW: We had text in earlier versions of
> > subscribed-notifications stating the need to support future types of
> > "notification messages" such as those defined in
> > draft-ietf-netconf-notification-messages.  However reviewers asked
> > these evolving references to be removed.
> >
> > We do have the option of importing terms from 6241 into the
> > NETCONF-notif document.  This would be the right place to do it
> > because in the subscribed-notifications document we want to limit any
> > introduction of NETCONF dependencies.  (Maybe NETCONF-notif adds text
> > to say that a "RFC6241 client" maps to subscriber, and "RFC6241
> > server" maps to publisher?)
> 
> 8342 defines the terms "client" and "server" in a transport-agnostic way.  I
> think we should try to use these terms in new documents, where applicable.
> In this document, the term "subscriber" is a special "client". 

Agreed.  Terminology section updated per the last email.

> I am not sure that a "publisher" is always a "server"; this needs to be decided.

I think that within YANG-push, a publisher is a special RFC-8342 "server".  Perhaps what we could add to YANG push in the terminology a sentence which says "In this document, the term publisher also includes the role of RFC-8342 server."    Alex, what do you think about that?

However my belief is that we shouldn't do a global cut-and-paste of "publisher" with some new term for this intersection to use throughout the document.   This could end up being confusing.  For example, if we define a new term like "YANG-push publisher" a reader of the YANG model would need to jump back and forth between the definitions of "publisher" and "YANG-push publisher" knowing that both are equally valid in this context. 
 
> > > If subscribed-notifications is transport-independent, it should
> > > probably not talk too much about <notifcation> etc; this should go
> > > into the transport docs.
> >
> > In general, this is what is done.  In subscribed-notifications, the
> > only place <notification> is mentioned at all is section 2.6.  If
> > necessary, we could move this section to NETCONF-notif, but that would
> > leave no transport independent framing for the notifications.  I guess
> > it is possible to live without that, but it would leave the
> > subscribed-notifications feeling incomplete.
> 
> If subscribed-notifications is transport independent, it should not have the
> NETCONF-specific text in 2.6.

RESTCONF also refers to RFC-5277's <notification>.   See section 6.4.    So there is precedent and adoption for reuse of the transport element beyond NETCONF.

So while pulling this section out and placing it within NETCONF-notif is possible, it would mean either replicating this information RESTCONF-notif, or forcing RESTCONF-notif to await the completion of  draft-ietf-netconf-notification-messages.

> 2.6 also says:
> 
>    In all cases, a single transport session MUST
>    be capable of supporting the intermixing of RPCs and notifications
>    from different subscriptions.
> 
> This applies to NETCONF, but not for the UDP transport, and I suspect not for
> the HTTP transport either?

Agreed.  This statement is now removed. 
 
> > I suspect a similar
> > thought process drove the inclusion of <notification> within RFC-6020
> > and then RFC-7950.
> 
> No; for various reasons YANG was initially positioned as a data modelling
> language for NETCONF only.  Hence all text about how to map YANG to
> NETCONF and XML.
> 
> > > 7950 says that the "notification" statement defines a notification.
> > > As Juergen pointed out this term is not defined in the terminology
> > > section, but nevertheless the term is used.
> > >
> > > Does the WG now want to introduce a new term for what the
> > > "notification"
> > > statement defines?
> >
> > It certainly might make sense to have a future update of RFC-7950 with
> > something like this.  I spend a bit of time trying to understand the
> > connection of YANG notification statement with <notification>.  Having
> > this be better defined would be helpful.
> >
> > >  It seems to me that the term "event record" is being proposed for
> > > this.
> >
> > An event record is not necessarily a YANG notification, as the event
> > record's payload might not be driven by the result of a YANG
> > statement.
> 
> I don't get this.  Can you give an example of when an event record is not
> defined as a YANG "notification"?

Another way to put this is that the event record within the <notification> might not be encoding YANG data.  For examples, all the <notification> within RFC5277 were defined before the availability of YANG.
 
> > > The answer to this question will have a big impact on the rest of
> > > the terminology.
> >
> > As event record has a larger scope than what can come from a YANG
> > notification statement, my suggestion would be for the revision of
> > RFC-7950 to import "event record", and then specify a new subtype term
> > (maybe "YANG event record"?).  If that term works, a YANG event record
> > could then be an event record where the contents are populated by the
> > results of the YANG notification statement.
> >
> > > > > Notification message - a message intended for a specific
> > > > > subscription
> > > receiver which includes one or more <notification>. A notification
> > > message will have undergone any security/content filtering on
> > > embedded <notification> as appropriate for that receiver.
> > > >
> > > > So how does this fit Figure 1 of RFC 6241? This figure indicates
> > > > that <notification> is a message as seen from the messages layer.
> > > > You are saying a notification message is something else that
> > > > includes one or more <notification>s. Yes, I know that the diagram
> > > > in RFC 5277 is different but the diagram in RFC 6241 is the newer one.
> > >
> > > This confuses me as well.
> >
> > The requirement for the bundling of many events is being driven by
> > large data center telemetry.  It is unclear at this point whether
> > NETCONF will be a transport used in this environment.
> >
> > If NETCONF does care about this environment, and does want to support
> > something like draft-ietf-netconf-notification-messages, I do think
> > tweaks to RFC-6241 will be needed.
> 
> Yes, somehow.

Ok

Eric
 
> > For example what is the definition
> > of <notification> within 6241, Figure 1 (right now point RFC-5277
> > isn't explicitly mentioned.).  Must this figure only be interpreted as
> > a RFC 5277 <notification>?  Can the figure also mean a
> > draft-ietf-netconf-notification-messages "message"?
> 
> RFC 6241 says that <notification> is defined in RFC 5277.  (ok, there's an error
> in there, and it points to 5717, but there's an errata for that).
> 
> > > How much of this do we have to define in this document, and how much
> > > should go into the transport docs?
> >
> > Beyond what I describe above, impacts would be to new/updated
> > transport drafts.  Plus an update to subscribed-notifications section
> > 2.6 to indicate that a new transport independent <notification>
> > construct exists.
> 
> Ok.
> 
> 
> /martin
> 
> 
> >
> > Eric
> >
> > > /martin
> > >
> > >
> > > > > Per the discussion below, I see an update record being a
> > > > > specialized type of
> > > event record.  For YANG push, the 'event' is driven by the update
> > > trigger: i.e.,
> > > either the expiration of a periodic timer (for periodic
> > > subscriptions), or a change to the datastore (on-change
> > > subscription).
> > > > >
> > > >
> > > > I am missing a definition what an Update record is. It is surely
> > > > not in this email. Anyway, if there are changes to architectural
> > > > concepts, it would be nice to find them in a coherent well explained
> section.
> > > >
> > > > /js
> > > >
> > > > --
> > > > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> > > > Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> > > > Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
> > > >
> >