Re: [netmod] Adoption poll for draft-wwx-netmod-event-yang

[Andy Bierman <[e-mail]>]

On Thu, Feb 27, 2020 at 6:30 AM Igor Bryskin <[e-mail]> wrote:

> Hi Andy, Jurgen, Alex and All,
>
> I believe that YANG could be a useful participant in a successful ECA
> framework if the following is kept in mind:
>
>
> 1. It is not feasible to realize an ECA framework relying solely on YANG.
> It is reasonable to expect ECA capable servers to support to a sufficient
> degree Xpath Expressions language and some sort of general purpose
> scripting  environment , such as Python, JunoScript, TCL/TKL, etc.;
>
>
I think some constrained scripting is required.
It is important that the WG understand the boundaries between
interoperability
and implementation choice.



> 2. ECA YANG model should define (and/or use definitions produced by other
> YANG models for) certain ECA components, such as Events, Policy Variables
> (PVs) and Actions (e.g. network re-configurations, client notifications,
> invoking of RPCs, etc.), but everything to do with Conditions and logical
> and mathematical expressions (which should be expected to be potentially
> very complex), should be left to XPath (i.e. configured as XPath expression
> strings). Although it is possible to define elementary micro conditions, it
> would be impractical (too tedious) for the clients to build conditions
> hierarchically (bottom up) and too cumbersome for the servers to process
> such constructs;
>


XPath +  PVs + new XPath functions might work.
Can this be done without reinventing components like alarms?
It would be way better to integrate existing models than create new ones
within ECA.
For example:

   event == generation of RFC 8632 <alarm-notification> event
   condition == script to extract relevant fields from event and check
condition
   action == script to use extracted fields from condition to send commands
to server

If the event stream management and event field extraction is standardized
(with YANG objects)
then that would help a lot. Access to metadata from the execution
environment (e,g, server) is also
important to standardize.



> 3.Likewise, it would be too demanding to expect servers implementing
> interpreters for specific purpose of interpretation of an ECA directly as
> it configured in YANG. Rather , it would be prudent to expect a server,
> upon receiving an ECA configuration, to generate out of it a micro-script
> in a locally supported scripting language and arrange said micro-script
> execution at the moment of the Event (or timer) firing;
>
>
This approach could help.
The "send RPC command" solution is too simplistic.
Maybe psuedo-code would work better.
Even a simple "edit" can be very different on each server (e.g., candidate,
running, defaults)



> 4. In short, the objective of the ECA YANG configuration is to provide a
> universal ECA representation that could be converted into a micro-script of
> the server's choice.
>
>
The implementation details are always a server choice.
I agree that mechanisms to bind ECA components to real scripting languages
has more promise than using YANG objects entirely, or creating a new
scripting language.


What do you think?
>
> Igor
>
>
Andy


>
>
> On Wednesday, February 26, 2020, 1:11:00 PM EST, Andy Bierman <
> [e-mail]> wrote:
>
>
> Hi,
>
>
> On Tue, Feb 25, 2020 at 5:57 PM Alexander Clemm <[e-mail]>
> wrote:
>
> In my view, an ECA model allows to define rules for events – conditions –
> actions, i.e. what actions to perform when an event occurs and a condition
> met.  A smart filter filters an input stream, letting some objects pass but
> not others.  They are not the same.
>
>
>
> There is a connection in that you could define the passing of an object by
> a smart filter as an event.  So, it is conceivable to include an ability to
> define events in this draft. If this is the intent it should be stated so
> clearly.  The question then becomes if you would want those be used also
> independently of the ECA model – there may be benefit in defining a new
> event without tying it to a rule (i.e. a condition and action) but simply
> emitting it..  (Same thing for the timer notification, which might have
> uses beyond ECA.) In the draft these things are all mashed together, but
> separating the ability to define an event from the ability to specify an
> ECA rule (which refers to / is triggered by an event) can benefit
> reusability.
>
>
>
> Anyway, as mentioned I think this work is relevant and I would like to see
> it go forward; IMHO some reframing and perhaps splitting of the draft
> should be considered whether that occurs before WG adoption or afterwards.
>
>
>
>
> I do not agree that refactoring this draft solves any adoption issues.
> YANG-based management already has events (specified with
> notification-stmt).
> The ECA data model should not duplicate other functionality such as alarms.
> Any event that can be received on an event stream (RFC 8639) should
> automatically
> be usable in any ECA logic.  Working on a solution without agreement on
> even the most
> basic ECA architecture or problem scope is a recipe for failure.
>
> Programming with YANG data models as the logic for conditions and actions
> has never been proven to work.  Even the trivial examples are complex
> and real-world use-cases seem near impossible. (nobody has ever provided
> one
> so we have to speculate). Achieving interoperability with a workable
> solution
> will not be easy. Other solutions have got "Hello world" to work, declared
> victory,
> and then went away forever.  Why will this time be different?
>
>
> Andy
>
>
>
>
>
> --- Alex
>
>
>
> *From:* Tianran Zhou <[e-mail]>
> *Sent:* Tuesday, February 25, 2020 4:44 PM
> *To:* Alexander Clemm <[e-mail]>; Joel Jaeggli <[e-mail]>;
> [e-mail]
> *Subject:* RE: [netmod] Adoption poll for draft-wwx-netmod-event-yang
>
>
>
> Hi the authors,
>
>
>
> >“Another one to allow the definition of custom events/notifications, or
> smart filters for push updates.  (We should bring back the earlier draft.)”
>
> As we worked on the smart filter before. We want to use the ECA model.
>
> It seems this model enabled the generic programmability. Can we just use
> it to program any filter or what potentially need to augment/customize for
> a specific model?
>
> Thanks,
>
> Tianran
>
>
>
> *From:* netmod [mailto:[e-mail] <[e-mail]>] *On
> Behalf Of *Alexander Clemm
> *Sent:* Wednesday, February 26, 2020 4:01 AM
> *To:* Joel Jaeggli <[e-mail]>; [e-mail]
> *Subject:* Re: [netmod] Adoption poll for draft-wwx-netmod-event-yang
>
>
>
> Hi,
>
>
>
> I support this draft and would like to see netmod work on this, but I do
> think some aspects need more maturing and parts of this probably should be
> rescoped.  Should the draft be adopted now, or should it be improved first
> and adopted later?  Not sure.  I would like to see the work continue, so in
> that sense I would clearly like to see the work adopted; at the same  time
> there are a number of issues that IMHO really need to be addressed.
>
>
>
> I share some of the concerns raised by Juergen and Andy.  Specifically, I
> think the precise problem needs to be defined more clearly.  In the
> discussion it was mentioned RMON – would it be that, or perhaps a better
> analogy Event MIB?  Section 3 mentions that this is to specify trigger
> conditions for when to send push updates.  That is perhaps consistent with
> an Event MIB, but a slightly different problem from ECAs.  Section 4.2 then
> proceeds to allow for the definition of “events” – but really only defining
> a “timer event”, with the ECA model omitting tie-in e.g. with
> notifications.  Including a threshold mechanism here is a bit distracting
> and should perhaps be taken out – while the crossing of a threshold might
> constitute an event, I don’t think this should be tied inside an ECA but be
> something that stands on its own.  (The prior draft on Smart Filters for
> Push Updates addressed this – it has layed dormant for a while and in this
> sense I can’t object for this work to be picked someplace else, but
> logically really it does not belong here but should be separate.)  The
> actions, finally, describe not simply management operations.  I understand
> the intent is to have an escape mechanism allowing to “call out” other
> functions / scripts deployed at a device, but this intent needs to be
> called out more clearly.
>
>
>
> So, in summary, I think the WG should consider rescoping this draft a bit
> – maybe divided into separate drafts, each addressing a separate concern,
> which will provide focus and make the problem being solved clearer:  One to
> define an ECA framework.  In this, clarify the invocation of actions, and
> allow for tie-in of notifications.  This would be this draft.  Another one
> to allow the definition of custom events/notifications, or smart filters
> for push updates.  (We should bring back the earlier draft.)  A third one
> to perhaps allow for the definition of “custom RPCs” that allow to invoke
> custom scripts/functions via Netconf/Restconf operations, then tie that ,
> which are then invoked using the regular RPC.  (This would be a new draft)
>
>
>
> --- Alex
>
>
>
> *From:* netmod <[e-mail]> *On Behalf Of *Joel Jaeggli
> *Sent:* Tuesday, February 18, 2020 8:44 AM
> *To:* netmod@ietf..org <[e-mail]>
> *Subject:* [netmod] Adoption poll for draft-wwx-netmod-event-yang
>
>
>
> This email begins a 2 week working group adoption poll for:
>
>
> https://tools.ietf.org/html/draft-wwx-netmod-event-yang-06
> <https://nam03.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-wwx-netmod-event-yang-06&data=02%7C01%7Calex%40futurewei.com%7Cf00fff51c8fb423b991208d7ba54f73b%7C0fee8ff2a3b240189c753a1d5591fedc%7C1%7C0%7C637182746419078457&sdata=IVHfOxhE7fTkLJ132TEGAM7mmIxdq2546iftp%2FbU5YE%3D&reserved=0>
>
>
>
> Please voice your support or objections before the poll completes on March
> 3rd.
>
>
>
> Thanks
>
> joel
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