Dynamic orchestration using multiple proxy services

Question

The project I am currently on is using ALSB for service orchestration. For a given orchestration, we would have one orchestration proxy (the control center), that synchronously calls a sequence of alsb proxy services.
Each proxy service in this second level fronts one or more business service calls to perform a specific operation ("Create Account", "Create User", etc.).
So far so good, all this can work just fine (and much of it is already working in production). The trick that I am trying to make happen currently, is to dynamically load the list of second-level proxies and loop through the list to trigger calls.
Loading a list of proxy paths/names is no problem, I have many options there. It's when I try to take that list and loop through it, calling each proxy on the list that I am stuck.
Unfortunately, it appears I could have three routing choices and none of them work:
1. Service Callouts only work with a static service name, not a dynamic one (so even if I had a for-each loop around a Service Callout action, it doesn't do me any good).
2. Dynamic Publish actions are asynchronous only
3. Dynamic Routing actions inside Route nodes work, except that only one can exist per proxy service.
Am I missing anything? Is there some way to get ALSB to accept dynamic synchronous invocation of multiple proxy services from one orchestration proxy service?
Meghan Pietila
Granite Consulting, Inc.
Minnesota

Answer 1

A way of Invoking a dynamically chosen proxy service (PS) synchronously could be the following.
Service Callout actions are synchronous, so ALSB will block in PS2 (PS=proxy service) when it does the invocation of PS1.
Assuming the following very simple scenario (I hope to have understood correctly your case):
OPS = orchestration proxy service
case1: OPS -> PS1 -> PS3 -> ...
case2: OPS -> PS1 -> PS2 -> ...
where each PSi calls one or more business service (I suppose that the business services called in each PSi are called in a predefined order), so what is changing from one case to another is the sequence of PSi to be called.
I've setup the following ALSB project:
- OPS proxy services
- PS1 .. PS4 proxy services
- a proxy called 'step'
- a xquery called 'routing'
The idea is to call, from OPS, another proxy (the 'step' proxy) in a synch way (service callout) passing the information of what proxy should be called dynamically.
In the 'step' proxy then I create the <route><service> XML fragment, for the Dynamic Route action. This <route><service> XML fragment will point to the configuration of yet another proxy service (PSx), that is the PSx that I want to call.
One limitation is that I assume that your OPS always calls for example 2 proxies which name is resolved dynamically.
About the xquery:
<routing>
<case name="1">
<node>PS1</node>
<node>PS3</node>
</case>
<case name="2">
<node>PS1</node>
<node>PS2</node>
</case>
</routing>
OPS performs the following steps:
- chooses what is the case: 1 or 2
- does 2 service callout to the proxy called 'step' passing each time the correct node to be called
$routing/case[@name=data($case)]/node[1]
$routing/case[@name=data($case)]/node[2]
In the 'step' proxy I do a dynamic publish to desidered PS:
<route xmlns="http://www.bea.com/wli/sb/context">
<service isProxy="true">{ $proxyToBeInvoked }</service>
</route>
where the proxyToBeInvoked variable is built from the node received by the caller.
I've used this approach in a solution currently under development but I've found some problems when I want to receive back in OPS the error raised by any PSi: I'm able to catch the error but I'm not able to receive back the detailed error like in an usual stack trace.
I hope that could be useful.
Regards
ferp