Re: [yang-doctors] [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10

"Eric Voit (evoit)" <evoit@cisco.com> Tue, 03 April 2018 22:32 UTC

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From: "Eric Voit (evoit)" <evoit@cisco.com>
To: Martin Bjorklund <mbj@tail-f.com>
CC: "netconf@ietf.org" <netconf@ietf.org>, "yang-doctors@ietf.org" <yang-doctors@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "draft-ietf-netconf-subscribed-notifications.all@ietf.org" <draft-ietf-netconf-subscribed-notifications.all@ietf.org>
Thread-Topic: [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10
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Date: Tue, 3 Apr 2018 22:32:53 +0000
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References: <20180323.123631.1717671339304960054.mbj@tail-f.com> <e989a39a44ea4938b2eb9a5686cf8dbc@XCH-RTP-013.cisco.com> <20180326.094758.1920158070824114086.mbj@tail-f.com> <20180326.102519.1083138646701275044.mbj@tail-f.com>
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Subject: Re: [yang-doctors] [Netconf] Yangdoctors last call review of draft-ietf-netconf-subscribed-notifications-10
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> From: Martin Bjorklund,  March 26, 2018 4:25 AM
>
> Hi,
> 
> BTW, I noticed this:
> 
>       leaf replay-log-creation-time {
>         if-feature "replay";
>         type yang:date-and-time;
>         description
>           "The timestamp of the creation of the log used to support the
>           replay function on this stream. Note that this might be
>           earlier then the earliest available information contained in
>           the log. This object is updated if the log resets for some
>           reason. This object MUST be present if replay is supported.";
>       }
> 
> I think the last sentence should be formalized, by adding:
> 
>    when "../replay-support";
>    mandatory true;

Done.   (Note that this stream info is config-false.)

Eric

> /martin
> 
> 
> Martin Bjorklund <mbj@tail-f.com>; wrote:
> > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > From: Martin Bjorklund, March 23, 2018 7:37 AM
> > > >
> > > > Hi,
> > > >
> > > >
> > > > "Eric Voit (evoit)" <evoit@cisco.com>; wrote:
> > > > > Hi Martin,
> > > > >
> > > > > > From: Martin Bjorklund, March 16, 2018 4:19 AM
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > Andy Bierman <andy@yumaworks.com>; wrote:
> > > > > >
> > > > > > [...]
> > > > > >
> > > > > > > 2.4.2.1.  Replay Subscription
> > > > > > >
> > > > > > >    If the "replay-start-
> > > > > > >    time" contains a value that is earlier than content stored
> within
> > > > > > >    the
> > > > > > >    publisher's replay buffer, then the subscription MUST be
> rejected,
> > > > > > >    and the leaf "replay-start-time-hint" MUST be set in the reply.
> > > > > > >
> > > > > > >    >> this is a significant and bad change from RFC 5277 behavior
> > > > > > >    >> the start-time says "send all events that you have stored
> > > > > > >       since this time" The server sends its oldest event and does
> > > > > > >       not reject the request.  This draft incorrectly interprets
> > > > > > >       the request as "the server MUST have an event stored at
> least
> > > > > > >       this old"
> > > > > >
> > > > > > I agree, and I have pointed this out in earlier reviews.
> > > > >
> > > > > In our past discussions, it looked like you were ok after
> > > > > reading Yves requirement here:
> > > > >
> > > > > https://www.ietf.org/mail-
> archive/web/netconf/current/msg12154.h
> > > > > tml
> > > > >
> > > > > Beyond this functional requirement, the design pattern used is
> > > > > that an establish-subscription RPC must send the exact
> > > > > parameters accepted by the publisher.
> > > > >
> > > > >
> > > > > > If a client sends a too early time, and the server doesn't
> > > > > > send the optional hint, the client will have to guess the
> > > > > > time.  Not very robust.
> > > > > >
> > > > > > If the motivation is that the client should be informed that
> > > > > > he might have missed some notifs b/c the replay-start-time is
> > > > > > too early, this information can be passed in the rpc-reply
> > > > > > from establish-subscription instead.
> > > > >
> > > > > Yes this could be done.  But this doesn't follow the design
> > > > > pattern of making the client explicitly ask for what they want.
> > > > > Consistent design patterns do matter.
> > > >
> > > > Well, "what they want" depends on the semantics of this leaf!  If
> > > > we keep the old semantics, then if the client passes this
> > > > parameter with some start time, it "explicitly asked for what it
> > > > wanted".
> > > >
> > > > Anyway, if the objective is to ensure that no notifs are sent
> > > > unless the replay-start-time exactly matches the event-time of a
> > > > notification in the buffer, then we can add a parameter to ensure
> > > > that.
> > >
> > > The current definition of replay-start-time is:
> > >
> > > "Used to trigger the replay feature and indicate that the replay
> > > should start at the time specified..."
> > >
> > > To me, that means the replay-start-time has to be covered by the
> > > scope of the replay buffer.  It does not mean that it is required
> > > that the requested replay-start-time needs to exactly match the time
> > > of a buffered event.
> >
> > The text is quite unclear:
> >
> >   Used to trigger the replay feature and indicate that the
> >   replay should start at the time specified.
> >
> > and:
> >
> >   If the "replay-start- time" contains a value that is earlier than
> >   content stored within the publisher's replay buffer, then the
> >   subscription MUST be rejected
> >
> > In lack of a clear definition, I assume that "content stored [in]
> > replay buffer" refers to event records, since I assume that nothing
> > else can be stored in the replay buffer?
> >
> > Next question is what it means that a time value is earlier than
> > "content"?  Again, my assumption is that it means "earlier than the
> > 'eventTime' of the event records".  Is this not what is intended?
> >
> > >From what you write here though, I think that what you propose is
> > that:
> >
> >   If "replay-start-time" is less than the latest of
> >   "replay-log-aged-time" and "replay-log-creation-time", then the
> >   request is rejected.
> >
> > This must be clarified.  Also, ensure that the required behavior is
> > clearly defined in the YANG module, and not just in the text in the
> > document.
> >
> > But I still think that there should be some way for the client to get
> > all buffered event records, just like what was supported in RFC 5277,
> > without extra round trips.  Note that if the system is quickly
> > generating notifs, the client might need many round trips before it
> > manages to replay anything.
> >
> >
> > > > In all cases, if the client receives a notif with a time later
> > > > than what it asked for, it knows that it might have lost some
> > > > notifs.
> > >
> > > Why would this mean it might have lost some notifs?  In the current
> > > embodiment, the replay will not start unless the subscriber asked
> > > for a time that is within the scope covered by the buffer.  I.e., a
> > > time later than both "replay-log-creation-time" and "replay-log-aged-
> time".
> >
> > See above.  But the reason for rejection is that the client might have
> > lost some notifs.
> >
> > > >   leaf replay-exact-start-time {
> > > >     if-feature "replay";
> > > >     when "../replay-start-time";
> > > >     type empty;
> > > >     description
> > > >       "If this parameter is present, and the server does not have any
> > > >        stored event record with 'eventTime' equal to the requested
> > > >        'replay-start-time', then the server MUST reject the request.";
> > > >   }
> >
> > If we add something like this, the leaf name and description text
> > needs to be tweaked for the clarified semantics of replay-start-time.
> >
> > > Something like this parameter *might* be applicable if we choose to
> > > respond to a dynamic replay request with events later than those
> > > requested.  (i.e., in the establish-subscription success response.)
> > > As noted in other threads, this is a legitimate way to approach the
> > > issue.  However if the WG chooses this way, this will result in an
> > > exception to the design pattern of requiring the subscriber to ask
> > > for what they are going to receive.
> >
> > I disagree.  The client explicitly asks the server to send all
> > buffered event records.
> >
> > > In addition, we might end up sending a stream of information to the
> > > subscriber which is not sufficient, and therefore not verifiably
> > > relevant.
> >
> > It is up to the client to define what is relevant.  Maybe I just want
> > to view the replay buffer for trouble shooting purposes.
> >
> >
> >
> > /martin
> >
> >
> > > > > > >    If a "stop-time" parameter is included, it MAY also be earlier
> than
> > > > > > >    the current time and MUST be later than the "replay-start-
> time".
> > > > The
> > > > > > >    publisher MUST NOT accept a "replay-start-time" for a future
> time.
> > > > > > >
> > > > > > >    >> MUST be later (if the start-time) if supplied
> > > > > > >    >> MAY be before current time?  Inconsistent with start-time
> > > > > > >       MUST have events that exist
> > > > > > >    >> MUST NOT accept future start-time different than 5277,
> but OK
> > > > > > >       because that was a bad requirement
> > > > > >
> > > > > > I have also pointed out in earlier reviews that the
> > > > > > requirement that the replay-start-time cannot be in the future is
> problematic:
> > > > >
> > > > > Yes.  The thinking both of you passed along drove this modification.
> > > > >
> > > > > >   I know that this text is also present in RFC 5277, but I think it
> > > > > >   needs to be changed.  Which current time?  Probably the
> server's,
> > > > > >   but how would a client know that?  This is a problem that we
> faced
> > > > > >   when implementing 5277.   I think we should remove this
> > > > > >   requirement, since it doesn't add any value anyway.
> > > > > >
> > > > > > IMO, if the server gets a replay-start-time that is later than
> > > > > > the latest stored notif, it will send a <replay-completed>
> > > > > > notif, and then move on.
> > > > > > This is a
> > > > > > very simple behavior that doesn't rely on synchronized clocks
> > > > > > or anything like that.
> > > > >
> > > > > The text which I suggested back to Andy :
> > > > >
> > > > >    If the "replay-start-time" is later the scope of time covered by the
> > > > >    replay buffer, then the publisher MUST send a "replay-completed"
> > > > >    notification immediately after the after a successful establish-
> > > > >    subscription RPC response.
> > > >
> > > > Good.
> > > >
> > > > > > [...]
> > > > > >
> > > > > > > 2.5.2.  Creating a Configured Subscription
> > > > > > >
> > > > > > >        In this case, when there is
> > > > > > >    something to transport for an active subscription, transport
> > > > > > >    specific
> > > > > > >    call-home operations will be used to establish the connection.
> > > > > > > When
> > > > > > >
> > > > > > >    >> is this normative or is callhome optional-to-implement?
> > > > > > >
> > > > > > >    With active configured subscriptions, it is allowable to buffer
> > > > > > >    event
> > > > > > >    records even after a "subscription-started" has been sent.
> However
> > > > > > >    if events are lost (rather than just delayed) due to replay buffer
> > > > > > >    overflow, a new "subscription-started" must be sent.  This new
> > > > > > >    "subscription-started" indicates an event record discontinuity.
> > > > > > >
> > > > > > >   >> this is confusing to send multiple "subscription-started"
> events.
> > > > > > >
> > > > > > >    To see an example at subscription creation using configuration
> > > > > > >    operations over NETCONF, see Appendix A of
> > > > > > >    [I-D.draft-ietf-netconf-netconf-event-notifications].
> > > > > > >
> > > > > > >    >> IMO the examples should be moved to this draft
> > > > > >
> > > > > > +1
> > > > >
> > > > > But those examples are transport specific.  This will make the
> > > > > document less applicable for other transports.
> > > >
> > > > I don't think it will.  Just write that the example is using
> > > > NETCONF XML or RESTCONF JSON or whatever.  Compare with the
> > > > RESTCONF draft, it has plenty of examples despite the fact that it
> > > > supports two encodings.
> > > >
> > > > I think having the examples in this draft is the right thing to do.
> > >
> > > For the RESTCONF draft, there isn't another natural matching
> > > transport document where the information naturally fits.  And by
> > > doing the split in this way means we can point to a fairly extensive
> > > list of examples in one place which is transport-relevant.
> > >
> > > Eric
> > >
> > > > > > > 2.7.1.  subscription-started 2.7.2.  subscription-modified
> > > > > > >
> > > > > > >   >> what is the value of returning all the input or configuration
> > > > > > >     parameters in these notifications?  For a dynamic
> subscription,
> > > > > > >     the only receiver just sent that info and does not need it.
> > > > > > >     For a configured subscription, that data can be read from
> > > > > > >     the configuration datastore.
> > > > > >
> > > > > > I agree.  Removing these redundant parameters would also
> > > > > > simplify the models quite a bit.
> > > > >
> > > > > I replied on the thinking here to Andy.
> > > > >
> > > > > Basically it is possible that you could only send the contents
> > > > > of the leafref for dynamic subscriptions.  However this
> > > > > introduces complexity, as should have a notification type and
> > > > > set a different expectation of what would be populated with a
> dynamic subscription.
> > > > > So in the end, we can do it.  But it makes the model more
> > > > > complicated (although the tree gets smaller.)
> > > > >
> > > > > Also this assumes that the receiver can do a read.  (For IoT,
> > > > > this might not be the case.)
> > > > >
> > > > > Beyond that, if the parameters change multiple times on a
> > > > > configured subscription, you might not be quick enough to do a
> > > > > read in time to know the parameters during a transient period.
> > > > >
> > > > > Finally, a configured receiver might have lost state, so why not
> > > > > refresh the full set?  There is little cost to refreshing the
> > > > > full view of the subscription.
> > > > >
> > > > > So in the end, this a complex simplification drives error cases
> > > > > and more variations to process for the receiver.
> > > > >
> > > > > > [...]
> > > > > >
> > > > > > > 4A) message encoding
> > > > > > >
> > > > > > >   feature encode-json {
> > > > > > >     description
> > > > > > >       "This feature indicates that JSON encoding of notification
> > > > > > >        messages is supported.";
> > > > > > >   }
> > > > > > >
> > > > > > >   feature encode-xml {
> > > > > > >     description
> > > > > > >       "This feature indicates that XML encoding of notification
> > > > > > >        messages is supported.";
> > > > > > >   }
> > > > > > >
> > > > > > >   identity encodings {
> > > > > > >     description
> > > > > > >       "Base identity to represent data encodings";
> > > > > > >   }
> > > > > > >
> > > > > > >   identity encode-xml {
> > > > > > >     base encodings;
> > > > > > >     if-feature "encode-xml";
> > > > > > >     description
> > > > > > >       "Encode data using XML";
> > > > > > >   }
> > > > > > >
> > > > > > >   identity encode-json {
> > > > > > >     base encodings;
> > > > > > >     if-feature "encode-json";
> > > > > > >     description
> > > > > > >       "Encode data using JSON";
> > > > > > >   }
> > > > > > >
> > > > > > >   typedef encoding {
> > > > > > >     type identityref {
> > > > > > >       base encodings;
> > > > > > >     }
> > > > > > >     description
> > > > > > >       "Specifies a data encoding, e.g. for a data subscription.";
> > > > > > >   }
> > > > > > >
> > > > > > >     leaf encoding {
> > > > > > >       type encoding;
> > > > > > >       mandatory true;
> > > > > > >       description
> > > > > > >         "The type of encoding for the subscribed data.";
> > > > > > >     }
> > > > > > >
> > > > > > >   >> IMO all YANG definitions related to message encoding
> should
> > > > > > >      be removed because they are in conflict with existing
> protocols.
> > > > > > >      NETCONF defines XML encoding. HTTP already defines
> > > > > > >      media type handling for message encoding (Accept, Content-
> Type)
> > > > > > >      There is no definition how to use JSON with NETCONF.
> > > > > >
> > > > > > +1
> > > > >
> > > > > Per response to Andy:
> > > > >
> > > > > It is true that it is possible to populate unsupported mixtures
> > > > > of protocol and encoding.  However:
> > > > > (a) for configured subscriptions, we must be able to select
> > > > > different encodings for a single type of transport
> > > > > (b) checking what is an invalid/unsupported combination for a
> > > > > platform is quite easy
> > > > >
> > > > > While it is possible to build a structure which enforces valid
> > > > > combinations with YANG, this would add complexity, especially as
> > > > > vendor custom encodings will also become new identities under
> > > > > the base encoding.  If there is some YANG structure which exists
> > > > > for such enforcement of protocol and encoding (which would be
> > > > > something likely common with other solutions), do you have a link?
> > > >
> > > > I replied to this issue in the other thread, so let's continue the
> > > > discussion there.
> > > >
> > > >
> > > > /martin
> > >
> >
> > _______________________________________________
> > Netconf mailing list
> > Netconf@ietf.org
> > https://www.ietf.org/mailman/listinfo/netconf
> >