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From "Vikas" <>
Subject Failover scenario in Synapse - FailoverMediator
Date Mon, 02 Jan 2006 11:23:29 GMT

I was trying to make a failover mediator up and running, here is a description of the stuff:

 * Failover Scenario
Say a service, has and
as backups in case it goes down or fails.
So if a request comes in for stockquotes, then the service is called,
if the reply is a fault then is invoked. If it also returns
a problem then is called. In case the last service also returns
a fault, the response sent to the consumer is a fault.
*The need
For failover to be performed by a mediator(assuming it has all the related data, like the
locations of the failover/backup services) it would need the original request that came to
*The difficulty
The message receiver [the default one in Axis2, used to send requests to the native services/Endpoints],
takes the request SynapseMessage, invokes the native service, gets the reply message (assuming
its a In-Out case). It then goes on to replace the request message's content with that of
the reply message, hence the original request is lost. If the first service fails then the
service invoked after it never gets the request message but only the fault message.
*The way-out
* Writing custom MessageReceiver for failover - This is highly AXIS2 based. In case we want
to hide our axis2 environment and give users a complete Synapse Experience, this would be
the least bit appreciative. Moreover, a mediator writer having to work with MessageReceivers
sounds no good.
This would be the safest option, to use a receiver which will fit the need. But is it feasible
and fits into the architecture, i.e. having different message receivers for different end
* Providing a clone option for the SynapseMessageContext - We can override the clone method,
and provide a SynapseMessage getCopy( ) method in the SynapseMessage's implementations. This
will be problematic as it could be misused also.
Am I walking the wrong path or missing something obvious??
Comments please..
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