Mark /
Bill
I
don't think anyone was advocating the mutlilayered approach ( of root and
sub-coordination ) within an enterprise / LAN ( Mark your comments about
performance are correct in this scenario ). The concerns being voiced regarding
performance at the f2f were about an A,B,C scenario where A,B and C reside in
different domains and the termination protocol had to follow the transaction
propagation through the services. The point I was making at the f2f was that the
transaction protocol and coordination should be separate from the invocation
trace (as it is the Choreology diagram Alistair put together
)
For
Example Service A invokes Service B that subsequently invokes Service C, the
coordination of a transaction is separate and does not need to follow the same
flow - i.e. A's coordinator can communicate with B and C's
sub-coordinators to terminate a transaction without relying on B to coordinate C
on its behalf.
To lay
this out explicitly the discussion as I remember centred around a chain
where Web Services A (initiator with root coordinator) calls Web Service B (
with sub-coordinator and multiple participants ) in a different domain, that
subsequently calls Web Service C ( with a sub-coordinator and multiple
participants of its own ). The question was whether the subcordinator in C
registers with the root coordinator in A or if the sub-coordinator in B masks
the relationship required for coordination between A and C. In my mind you
should allow B to decide if it wants to mask C or not i.e. propagate its own
sub-coordinator to C or the root-coordinator from A that was propagated to it.
There
are some issues to do with security in this model surrounding C gaining access
to A ( I think a concern that Bill you brought up) . This is a valid concern but
I think there are ways to address this in terms of; if C tries to register with
A's coordinator then if the request contains transactional context recognisable
by the root coordinator at A and can accept a URI of the subordinator at C, are
there concerns here? I would make the case that A's root coordinator now sends
the appropriate termination message to C (the URI provided, through the BTP
termination protocol to C that has declared its ability to be BTP aware through
its registration) as they are enlisted - if C is bogus why does A care, and how
did C get a GUID identifier for the transaction initiated by A ( it must have
been through a trusted partner ).
I am
not suggesting there are not other concerns surrounding this and I am sure there
is need for further discussion on Security and the implications of the model,
but I do agree that based on role definitions the use of "interposition" as Mark
laid out, this is an appropriate model to be supported by
BTP.
I
think there was a lot of discussion at the meeting that blurred the lines
between the Service, Sub-Coordinator and Participant roles ( especially between
the Choreology guys Salas and myself ). I am now wondering if we have to
explicitly define the role of sub-coordinator distinct from Participant ( when
arguing last week for participant enrollement I was arguing for multiple
participant registrations to the coordinator (root) based on the Participants
that reside in different trusted domains and act as sub-coordinators for
all the sub-participants associated to the service invocation, within their
domain ).
I think we are all in agreement or at
least close.....unless I missed something.
-----Original Message-----
From: Bill Pope
[mailto:]
Sent: Monday, April 30, 2001 10:23
AM
To: 'Mark Little'; bt models
Subject: RE: interposition
requirements
I
agree with you and so won't try to defend the position. Just wanted to
set the stage for the discussion. I don't remember
who
was advocating this at the meeting, anyone?
Regards,
=bill
-----Original Message-----
From: Mark Little
[mailto:]
Sent: Monday, April 30, 2001 12:57
PM
To: Bill Pope; bt models
Subject: Re: interposition
requirements
Mark,
One thing I forgot to include in my original
reply. There are two places that BTP might be used. To
coordinate calls among disparate, external web services and to coordinate
calls to XML based services within an organizational boundry.
The registration of sub-participants with the root coordinator was being
proposed as an optimization for the latter.
If all Web Services are within the same domain (e.g., on the same LAN),
then there's no performance advantage, but I don't think there's much of a
performance disadvantage either in this world of modern, multi-threaded
operating systems. In addition, if multiple services happen to be co-located
on the same node as a subordinate coordinator then intra-node communication
is typically short-cut by the OS so that it doesn't go anywhere near the
network. (BTW, I'm assuming that a single organizational boundary is
connected only be a fast LAN, otherwise the communication performance
argument comes back in.)
However, in the arena of a single organizational boundary I'd still say
that the separation of concerns, and isolation of business logic is
important: why should the root coordinator know about sub-participants?
That's implementation specific. Even within an organizational boundary, one
department may not trust all of the Web Services from another, and may not
want root coordination information to be propagated around the
organization.
I would prefer us to keep things simple and have interposition as the
default, and if an application wants to register a service directly with the
root, then it can do it at the application level.
Cheers,
Mark.
-----------------------------------------------------------------------
SENDER
: Dr. Mark Little, Architect (Transactions), HP Arjuna Labs
PHONE :
+44 191 206 4538, FAX : +44 207 670 1964
EMAIL :
