I mentioned this at the interim but only briefly. It seems to me that we're
getting our service binding times wrong. This may be an artifact of my
confusion over whether we're discussing the Admin Service (AS) or the
Transit Intermediary (TI) when we discuss rules.
In the architecture to-date, we say that the XML form of the rules are used
both between the rule "owners" and the AS and between the AS and TI. In the
actions, we bind to a specific instance of code.
I believe this early binding is completely inappropriate for at least some
of the rule owners who more than likely have no need nor desire to know
about the decisions made in a CDN regarding function distribution. It is
more reasonable, I think, but still undesirable for the TI rule base to have
these bindings specified in the rules. IMHO, there's entirely too much
discussion about requirements for APIs (this is the IETF after all) but it
seems that there's one late binding semantic that's needed in the
architecture model: resolving a service name to its location and making the
appropriate call to the service (i.e., over a protocol, e.g., ICAP or BEEP,
or a local call to an x-let or library service). One of the principle
benefits of policies in a network environment is their scalability; you
loose that scalability when you bind too early.
BTW, this late binding argues for at least having a set of semantics defined
for use on the OPES platform if not a real API.
Assuming, for the purposes of discussion, that we agree with the above
assessment, the question of whether we care if an x-let is typed on the
basis of the APIs on which it depends (which, I believe, is the better way
to think about them) or where it happens to run, becomes a smaller question
since it doesn't show up in the rules but only in the architecture and
implementation details for service invocation and, perhaps, in the meta-data
if we choose to bind service name to URL there.
Lee M. Rafalow
Voice: 1-919-254-4455; Fax: 1-919-254-6243
IBM Internet Technology Management
IBM Corporation
P.O. Box 12195, BRQA/502
RTP, NC 27709 USA
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Home email: rafalow(_at_)mindspring(_dot_)com