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

"Eric Voit (evoit)" <evoit@cisco.com> Fri, 15 June 2018 13:25 UTC

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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>, "Zhengguangying (Walker) (zhengguangying@huawei.com)" <zhengguangying@huawei.com>
CC: "alexander.clemm@huawei.com" <alexander.clemm@huawei.com>, "alex@clemm.org" <alex@clemm.org>, "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: Fri, 15 Jun 2018 13:24:56 +0000
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Subject: Re: [Netconf] comments on draft-ietf-netconf-subscribed-notifications-12
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> From: Martin Bjorklund, June 15, 2018 4:49 AM
> 
> "Eric Voit (evoit)" <evoit@cisco.com> wrote:
> > > 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."
> 
> Can we first agree on the basic terminology in subscribed-notifications?
> 
> First question: are server and publisher potentially different entites or not?

Yes.  Here is my reading:

(a) A publisher sending YANG formatted notifications will be an RFC-8342 server.  

(b) A publisher sending non YANG formatted notifications (e.g.,  XSD) will not be an RFC-8342 server. 

(c) An RFC-8342 server might not be a publisher.

(d) An RFC-8342 server that supports at least one YANG model using the notification statement, and which also supports subscribed-notifications will be a publisher.

> Looking at restconf-notif, it seems to me that the publisher is an
> HTTP2 client, i.e., a different entity than the RESTCONF server.

For configured subscriptions, there is no RESTCONF.  The publisher is just an HTTP2 client.

For dynamic subscriptions, the publisher is both a RESTCONF server and HTTP2 client.  (Note: this is the closest IETF match to what GRPC might be able to transport that I can see.)

> Is this correct:
> 
> NETCONF:
>    subscriber is a NETCONF client
>    publisher is a NETCONF server
>    receiver is a NETCONF client

Yes

> RESTCONF
> 
>    subscriber is a RESTCONF client
>    (NOTE 1)
>    publisher is a HTTP2 client
>    receiver is a HTTP2 server

Yes

Also note that Andy also wants HTTP1.1 support for dynamic subscriptions.  And while this is in Section 3.5 of document, personally I don't think it worth inclusion.  This is a debate we should have for that draft.
 
> UDP
> 
>    subscriber is a NETCONF/RESTCONF client
>    publisher is a UDP client
>    receiver is a UDP server

Walker, can you comment on this?  It hits on the terminology diagram discussion over the last few days.

> NOTE 1: the RESTCONF server is missing from this picture.  It doesn't have a
> special term...
> 
> 
> I assume this work is not applicable to CoMI?

It is applicable to CoMI.   See:
https://tools.ietf.org/id/draft-birkholz-yang-push-coap-problemstatement-00.html

Eric

> /martin
> 
> 
> > 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/>
> > > > > >
> > > >
> >