I'd like to pick up on Charles' use-case to validate my understanding
and possibly define some kind of best practice within JBI since I see
this pattern come up quite frequently.
To summarize, we have the following environment:
* One consumer component (MyConsumer)
* One routing component (MyRouter)
* Several service provider components (ServiceA, ServiceB, ...)
implementing the same service type (SameInterface)
What we want is to have a processing pipeline that dynamically picks up
one of the service provider components based on a policy defined in the
routing component:
MyConsumer --> MyRouter --> { ServiceA or ServiceB or ... }
My questions are 1) what are the requirements for each components
and 2) what's the best way to achieve this?
For the sake of identifying the bounds of the JBI specification and the
added-value of ServiceMix, I'd like to answer those question both for a
"plain-vanilla" JBI container and for ServiceMix v2.x.
First, I assume all components must handle the message exchange pattern
defined by the service type (e.g. one-way, request-response, ...).
Otherwise, I don't think the exchange could be carried out successfully.
Now, is it a requirement of the JBI spec that MyRouter expose
SameInterface on the JBI bus using ComponentContext#activateEndpoint and
subsequently Component#getServiceDescription? If so, does ServiceMix
require this as well?
I'm going to go out on a limb now and say that MyConsumer cannot be
(deterministically) linked to MyRouter by relying on service type
routing because we have more than one component exposing SameInterface.
Thus, MyConsumer must specify MyRouter's fully qualified service
endpoint name. Is this right?
Based on section 5.4.3.3 of the JBI specification, the service endpoint
name can be a hard link, a soft link or a standard link as determined by
in the service unit's meta-data. I guess the choice between those is a
deployment preference. I'd be curious to hear from people who have
experience about which approach work best for them.
I'll assume MyRouter is driven by some sort of business policy, such as
content-based routing. For example, the policy could be "route all
transactions under $1000 to ServiceA and those equal or over $1000 to
ServiceB." MyRouter must therefore be configured with rules and with
service endpoint names of ServiceA, ServiceB, etc.
Once again, is it a requirement of the JBI spec that service provider
components (ServiceA, ServiceB, ...) expose SameInterface on the JBI
bus? And if so, does ServiceMix enforce this?
Is what I described here a good design? Is there a simpler way of going
about it using plain JBI? I understand ServiceMix simplifies the
configuration of such pipeline using Spring+XBean but I'd like to
understand as well the actual requirements if the same components were
to be moved to another JBI container.
Another question I have is whether it would be advantageous to hook a
policy at the NMR level instead of having a routing component on the JBI
bus.
Thoughts or comments anyone?
alex
Guillaume Nodet wrote:
JBI provides some way to specify routing at deployment time, but not at
runtime using the jbi.xml configuration file.
If you want to do advanced routing in servicemix, there are two ways:
* either implement an EndpointChooser and set it on the activation
spec, or use it as the default one : the main problem is that
they can not be updated at runtime. We currently have very basic
policies : FirstChoicePolicy and RandomChoicePolicy.
We may be able provide more advanced policies, but it is imho quite
difficult to come up with generic policies.
If you have ideas about generic policies to implement, please tell
us so that we can discuss them.
You can also raise a jira and attach a patch when you have written
one :)
* using a service engine as a router : the main benefit is that by
undeploying / redeploying, you can change the routing policy.
This can be done using rules engines, such as drools, or xslt
routers. We can also imagine using an external store and retrieve
the updated policies on a regular basis. The deployment would only
consist on a pointer to a set of rules in the external store.
I think that if the routing rules contains business logic, this should
be handled by a service engine and not a policy, to be able to
manage them easily using jmx. Policies imho, should be kept for simple
policies that can not fail, but this may be argued I guess.
Cheers,
Guillaume Nodet
Charles Souillard wrote:
I now well understand your explanation.
It helps me.
But I am surprised there no way to map OilProvider one time to Total
and another time to Elf...
Perhap I will work with Total for 1day and then move for 2 days to Elf
etc...
I am surprised to only have the solution to remove the SE !
I can also imagine I have many oil products and that I want to ship
15W40 oil to Elf and 15W50 to Total so I need to have both at the same
time !
What I was thinking is a way to configure JBI container to move from
one to the other very quickly. Perhaps this info could be carried in
the message sent through the NMR. Both Elf and Total implement
OilProvider...
What do you think about that ?
Regards,
Charles
