Title: Re: [ebxml-msg] an assessment of the reliability of pulled messages
Correct.
I
believe that works well (except for the fact that this case would deserve more
exposure in WS-Reliability )
Inline
comments:
-----Original Message-----
From: Jeff Turpin
[mailto:]
Sent: Friday, December 10, 2004
9:01 AM
To: Jacques Durand;
''
Subject: Re: [ebxml-msg] an
assessment of the reliability of pulled messages
So
basically the exchange would look like this:
ebMSH A
ebMSH
B
PullRequest
-------------------> (SOAP Request - "Request/Response MEP") -------->
(w/
WSRM Request)
[Jacques Durand] reliable Pull with response reply pattern.
<----------------------------------(SOAP
Response - "Request/Response MEP")------Queued ebXML Message (Pull
Response)
(w/
WSRM Response & WSRM Request)
[Jacques Durand] reliable SOAP
response (callback pattern only) bundled with an Ack (this is not precluded by
WS-Reliability, but not much advertized
either)
WSRM
Response (Callback)
------------------------------------------------------------->
Is
this correct? I apologize for my crude diagram, I hope it comes through
ok.
[Jacques Durand] Important note: the Pull message should
also require NoDuplicateDelivery, so that the behavior specified in WS-R 3.2.2
applies: if the sending RMP does not get the expected pulled message for
whatever reason (note: an "empty" ebMS response message due to no message
available to pull is a valid response for the sending RMP, so is
excluded from the case I describe here)
then the sending RMP will resend the Pull. In case the
failure occurred during the transmission of the pulled message (receiving RMP
had actually received the initial Pull and passed it to ebMS MSH and
gotten the pulled message ) then we expect the receiving RMP to resend a
copy of the initial pulled message that it had cached, for each Pull resent.
So we should not need the "idempotency" assumption for Pull
messages.
Jacques
Jeff
On 12/8/04 8:06 PM,
"Jacques Durand" <>
wrote:
About
relying (after all) on WS-Reliability for ensuring the guaranteed delivery
of pulled messages (ebMS Pull responses):
-------------------------------------------------------------------------------------------------------------
One of the reasons we did not consider this was the fact
that this reliability case falls
under
the more general reliability of [synchronous] response messages
(speaking in terms of SOAP MEPs)
and we
knew that this is something WS-Reliability will very likely have to address,
but in the next release.
Having now a second look at this,
and at how much interpretation leeway WS-Reliability 1.1 would allow for
this:
First, summarizing the best we can hope for:
-
ensure guaranteed delivery of pulled messages in the same way as for any
other message,
but with a resending mechanism that includes the Pull
signal (since we can't just resend the response).
- in
case of delivery failure, the pulled party will know and notify its Producer
party the same way
as for pushed messages that
fail.
- we get all this without introducing new ebMS signals
(e.g. an Ack for pulled messages)
And then looking at how well WS-Reliability 1.1 can
handle this:
- It is clear that the resending
behavior can't be same for pulled messages as for pushed
messages.
WS-R 1.1 states (3.2.1) that "a resending technique MUST
be used ... [ for messages under GuaranteedDelivery
agreement)"
but is
not more specific. So it can be interpreted as resending of the Pull ebMS
signal (which would cause
resending of the cached pulled message).
More on this later.
- the Reply Patterns as defined in
2.4 do not preclude "reliable" responses (of a SOAP request-response MEP)
that
have themselves wsrm:Request headers (of course, a
"response" reply pattern would not make sense here)
-
Which RMP operation is used for submitting a "reliable" pulled message is
TBD. DO not see major issue here though
would
need be clarified by implementors. Both Respond and Submit seem open (yet
reliability of Respond unspecified.)
Conclusion: Reliability of pulled messages is certainly
underspecified in WS-Reliability 1.1
meaning it is not precluded, but
1.1 is mute about associated restriction(s)
(e.g. about usable reply
patterns, related faults)
Certainly WS-Reliability implementors
would have to be aware that these features are needed in addition to what
1.1 requires, for use in ebMS.
One
more word about the resending mechanism for the Pull:
-
It has been suggested in the meeting this afternoon that a Pull resending
could be handled at ebMS MSH level.
I
would advise against that for several reasons.
First, nothing prevents a
pulled message to have both wsrm:Request header and wsrm:Response header for
acking of the Pull.
So I
would just rely on guaranteed delivery of the Pull message itself and
associated resending at RMP level.
Then,
the Pull is not really idempotent (ebMS queue management).
Also:
the pulled party is waiting for an Ack that targets the pulled message that
was initially submitted to RMP.
The receiving RMP can associate
successive resends of a Pull request with this same (cached) pulled
response,
but only if the resending is done by sending RMP (if done
by MSH, would look as different requests for receiving RMP,
mandating different responses - at least looking
different from RMP viewpoint - each of these asking for a different
Ack).
Correct interpretation of a Callback Ack for these
copies, and correct delivery failure notification to the pulled party
depends on this.
-Jacques
