Can I open a clustered MQ queue for writing in Perl?

Question

If I have a Websphere MQ queue defined on another queue manager in the cluster, is there a way I can open it for writing using the Perl interface? The code below brings back mqrc 2085.

$messageQ = MQSeries::Queue->new
        (
         QueueManager         => $qMgr,
         Queue                => $queue,
         Options              => $openOpt
         ) or die ">>>ERROR2: Unable to open the queue: $queue\n";
}

Answer 1

Yes! The Perl modules are a thin veneer over the WMQ API and expose all the basic options and most of the really esoteric stuff as well.

When you open a queue, WebSphere MQ performs name resolution on the values you provide for Queue and QMgr names. If you provide both a Queue and a QMgr name then the object reference is fully qualified and WMQ will attempt to open it as named. So if the name you provide is the local QMgr and the clustered queue does not have a locally defined instance, the open will fail with a 2085 Unknown Object Name.

The trick to opening a clustered queue is to provide a null value for the QMgr name. This causes name resolution to check the local QMgr for a queue of the same name, then finding none it checks the cluster repository and resolve the open to the clustered queue. Note that the queue must be advertised to the cluster for this to work. Specifically, the CLUSTER or CLUSNL attribute of the target queue must be non-blank and refer to a cluster that the source QMgr participates in. Similarly, the destination QMgr must also participate in the same cluster as the source QMgr.

Note also that if you specify a QMgr name on the open that is not the local QMgr, then WMQ will attempt to resolve the QMgr name only. If it can resolve a route to that QMgr then it will send the message there. This means that in a cluster you can send a message to any queue on any QMgr so long as you know the fully-qualified name.

Finally, you can define a local alias over a clustered queue. For example if you are on QMGRA and DEF QA(TARGET.QUEUE) TARGQ(TARGET.QUEUE) and then on QMGRB and QMGRC in the same cluster you DEF QL(TARGET.QUEUE) CLUSTER(MYCLUS) then it is possible to open QMGR=QMGRA QUEUE=TARGET.QUEUE and still have it work as expected. Note that the alias is NOT advertised to the cluster but the target queue is. The only issue with this approach is that the first time it is opened the API call may fail if the cluster query takes too long. When I do this in Production, I always use amqsput on the alias ahead of time to make the QMgr query the repository before the actual application opens the queue. Why would you do this? If security is a concern you probably don't want to authorize all apps directly to the cluster XMitQ because, as noted above, they could then put a message onto any queue on any QMgr in the cluster, including SYSTEM.ADMIN.COMMAND.QUEUE. The alias gives you a place to hang authorizations and restrict the user to specific destinations in the cluster.

So short answer, make sure you provide a null QMgr name on the Open call or set up a local alias over the clustered queue. For more about the security aspects of this, see the WMQ Security presentation at http://t-rob.net/Links