Re: [CDNi] footprint and capability mechanisms

[Jan Seedorf <[e-mail]>]

Dear Jon,

Thank you for the good and fair summary below, this is pretty much the status quo. Just one comment: the reason why some of the necessary ALTO extensions have been delayed is that the ADs/chairs have disallowed such work to be discussed before the core ALTO protocol has been published; just recently green light for continuing work on extensions has been given.

What in my view it boils down to (as you highlight below):
-- ALTO has error handling, encoding, security worked out (pro for using ALTO)
-- incremental and asynchronous updates for ALTO is early stage; in fact the ALTO WG is right now re-chartering to add those two items to the charter item list, early work exists, but it will take some time for those specs to be ready (con for using ALTO)

What Richard and I have in mind was to drive these very-soon-to-be-on-the-chartered ALTO extensions (i.e. incremental/asynchronous updates) by the concrete CDNI FCI use case. In other words we intend to define a solution for CDNI/FCI and kick that back into the ALTO WG. But no doubt, having these ALTO extensions done in ALTO will likely take longer than the current CDNI milestone for the FCI solution spec.

Kevin, all: anything you want to share to the discussion?

 - Jan

> -----Original Message-----
> From: CDNi [mailto:[e-mail]] On Behalf Of Peterson, Jon
> Sent: Thursday, February 06, 2014 7:41 PM
> To: [e-mail]
> Subject: [CDNi] footprint and capability mechanisms
> 
> Following our discussion about the FCI mechanism in Vancouver, I took a
> look at two drafts out there today: draft-ma and draft-seedorf. In short,
> I think both express promising directions, and both have a long way to go
> before they will describe fully fleshed-out mechanisms. At a high level,
> their architectures are similar: both are about pushing JSON objects that
> describe footprints and capability via HTTP. It¹s often when the choices
> are so similar that it¹s hardest to figure out which is the right approach.
> 
> One of the prominent distinctions between the two is that Kevin specifies
> a capability-sharing system with an optional footprint, whereas Jan
> specifies a footprint-sharing system with the option of capabilities.
> Jan¹s choice is an artifact of using ALTO as a basis, which already has a
> concept of sharing 'network maps' in this fashion, and can be extended to
> add further information to these maps such as capability. Kevin works from
> the ground up on a bespoke system for sharing capabilities, which may not
> ever involve sharing footprint data. I¹ve turned this over in my head a
> bunch of times, and I¹m not really sure there¹s any practical advantage
> one approach has over the other. One of the non-obvious reasons why is
> that the concept of a PID (the groupings of network elements) in ALTO is
> so abstract that it serves as a layer of indirection, and can serve as a
> placeholder for a footprint that¹s effectively specified implicitly.
> 
> An important feature we want this mechanism to have is incremental FCI
> updates. Both Kevin and Jan have a story about this, though I think both
> will require substantial work to advance. Kevin, for example, sketches a
> system of primitives (replace, include, exclude) to allow a dCDN to update
> a uCDN about changes, based on tracking update sequencing with a new
> 'CDNI-FCI-Seq' HTTP header. State freshness of web resources is a pretty
> thoroughly-studied problem, though, and there are other HTTP facilities
> (Etags, say) that address this. I think it¹s pretty unlikely that our
> problem is enough of a special case that we could convince Application
> folks here at the IETF that we need to standardize a custom HTTP header
> for it. Jan¹s draft, on the other hand, references existing ALTO work on
> incremental updates, in particular draft-schwan-alto-incr-updates. That
> draft contains a good overview of the different approaches, including HTTP
> If-Modified-Since and Etags, as well as looking at JSON-specific
> incremental change techniques like JSON Patch (RFC6902). Sounds great, but
> - draft-schwan is currently an expired I-D (for like a year), and it is
> really more of a survey than a draft that makes a concrete recommendation.
> This work would need to be resumed and made far more concrete for this to
> be a viable approach.
> 
> Asynchronous updates are another very important feature. We don¹t want
> to
> force uCDNs to poll dCDNs, we want dCDNs to be capable of asynchronously
> notifying uCDNs when a change to network state happens. Kevin again has a
> sketch of a solution here, where capability information can either be
> acquired by a GET from the uCDN or a POST by the dCDN. While as described
> it is very lightweight, I suspect it¹s probably a bit too lightweight: I¹d
> want to know a lot more about how resource identifiers are discovered or
> formulated, and a ton more about error-handling and security. This
> mechanism almost certainly should be ReST-based, as it will then inherit
> many of the right principles. ALTO, based on Jan¹s draft, of course is
> already ReST-based, and has exhaustive sections on JSON encoding, errors,
> security, and the way to formulate queries via POSTs. What it lacks is an
> asynchronous publication capability. Once again, there are some I-Ds we
> can point to, but nothing I¹d consider very concrete. Worse still, even
> the capability data that ALTO might carry is based on a -00 I-D
> (draft-roome-alto-pid-properties) which is very sketchy, to the point
> where providing even a mock-up of the JSON encoding for capabilities in
> ALTO is probably impossible today.
> 
> So where does this leave us? Fleshing out either of these approaches will
> take work. We don¹t want to do needless work articulating two proposals
> where we only need one. It is however difficult to have a serious
> discussion about the advantages of either mechanism when they are only
> specified to this limited degree. Ideally some kind of merger would be
> possible here, and the sooner we can get to that the better. I don¹t think
> the baseline JSON formats for rendering either footprints or capability
> will ultimately vary significantly in the two proposals. It then just
> becomes a question of whether it is more practical to start tabula rasa,
> as Kevin does, or to build on an existing mechanism, as Jan does. ALTO
> comes with baggage, but that baggage has accumulated from several years
> now of comment and review, and surely a lot of those components (like
> error handling, encoding, security) would have to be incorporate into
> Kevin¹s draft if we went forward with it. I suspect that would ultimately
> be a longer path, but neither of these paths are particularly short.
> 
> Jon Peterson
> Neustar, Inc.
> 
> 
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