Routing MSMQ messages from one queue to another
Is there some standard configuration setting, service, or tool that accepts messages from one queue and moves them on to another one? Automatically handling the dead message problem, and providing some of retry capability? I was thinking this is what "MSMQ Message Routing" does but can't seem to find documentation on it (except for on Windows Mobile 6, and I don't know if that's relevant).
Context:
I understand that when using MSMQ you should always write to a local queue so that failure is unlikely, and then X should move that message to a remote queue. Is my understanding wrong? Is this where messaging infrastructure like Biztalk comes in? Is it unnecessary to write to a local queue first to absolutely ensure success? Am I supposed to build X myself?
Answer
As Hugh points out, you need only one MSMQ Queue to Send messages in one direction from a source to a destination. Source and destination can be on the same server, same network or across the internet, however, both source and destination must have the MSMQ service running.
If you need to do 'message' routing (e.g. a switch which processes messages from several source or destination queues, or routing a message to one or more subscribers based on the type of message etc) you would need more than just MSMQ queue. Although you certainly can use BizTalk to do message routing, this would be expensive / overkill if you didn't need to use other features of BizTalk. Would recommend you look at open source, or building something custom yourself.
But by "Routing" you might be referring to the queue redirection capability when using HTTP as the transport e.g. over the internet (e.g. here and here).
Re : Failed delivery and retry
I think you have most of the concepts - generally the message DELIVERY retry functionality should be implicit in MSMQ. If MSMQ cannot deliver the message before the defined expiry, then it will be returned on the Dead Letter Queue, and the source can then process messages from the DLQ and then 'compensate' for them (e.g. reverse the actions of the 'send', indicate failure to the user, etc).
However 'processing' type Retries in the destination will need to be performed by the destination application / listener (e.g. if the destination system is down, deadlocks, etc)
Common ways to do this include:
- Using 2 Phase commit - under a distributed unit of work, pull the message off MSMQ and process it (e.g. insert data into a database, change the status of some records etc), and if any failure is encountered, then leave the message back onto the queue and the DB changes will be rolled back.
- Application level retries - i.e. on the destination system, in the event of 'retryable' type errors (timeout due to load, deadlocks etc) then to sleep for a few seconds and then retry the same transaction.
However, in most cases, indefinite processing retries are not desirable and you would ultimately need to admit defeat and implement a mechanism to log the message and the error and remove it from the queue.
But I wouldn't 'retry' business failures (e.g. Business Rules, Validation etc) and the behaviour should be defined in your requirements of how to handle these (e.g. account is overdrawn, message is not in a correct format or not valid, etc), e.g. by returning a "NACK" type message back to the source.
HTH