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From Fraser Adams <fraser.ad...@blueyonder.co.uk>
Subject Re: Messaging Flow Design in Qpid
Date Wed, 02 May 2012 18:36:00 GMT
Hi Matthew,
I think that "technically" the answer is "no" however you could use 
federation (with a little teeny bit of tweaking).

So it's possible to use qpid-route to federate between two brokers 
however there's a line in qpid-route that throws an exception if you try 
to do this -it moans about linking on the same host.

However...... the broker actually happily allows this.

I hacked the qpid-route addLink method thus...

     def getLink(self):
         links = self.agent.getObjects(_class="link")
         for link in links:
             if self.remote.match(link.host, link.port):
                 return link
         return None

     def addLink(self, remoteBroker, interbroker_mechanism=""):
         self.remote = BrokerURL(remoteBroker)
         #if self.local.match(self.remote.host, self.remote.port):
         #    raise Exception("Linking broker to itself is not permitted")

         brokers = self.agent.getObjects(_class="broker")
         broker = brokers[0]
         link = self.getLink()
         if link == None:

So literally just commented out the test for self.local.match and the 
raise Exception and it works - one can federate from one exchange to 
another on the same broker.

It's slightly controversial :-) but I wanted to see if it was possible. 
You'd want to be careful to avoid circular routes etc.

But this approach might be what you're looking for unless someone can 
come up with a better mechanism.

BTW federation only works with the C++ broker IIRC correctly so this 
might be an issue for you I believe that you were planning on using the 
Java broker (which gives you broker side message selectors) :-/


On 02/05/12 18:42, m.luchak@smartasking.com wrote:
> Hi All,
> Thanks for all your help with the selector questions that I had last week.  We are conducting
more tests to see if Qpid is the solution for our architecture but we have some doubts...Our
flow requires that exchanges subscribe to exchanges and queues in turn subscribe to multiple
> 1) Is it possible to bind Exchanges to Exchanges?  I have seen some posts giving an emphatic
NO: ([http://qpid.2158936.n2.nabble.com/how-to-bind-exchange-to-exchange-like-bind-exchange-to-queue-in-the-same-broker-td6385448.html]
> 2) The x-binding syntax , that I have encountered, for binding a queue to multiple exchanges
seems a little convoluted and the last time I asked you guys for help I discovered wonderful
new simplified classes and methods :).  Is the following example the best practice for creating
multiple bindings?
> x-bindings:[{queue:MYQUEUE,exchange:'FIRST_EXCHANGE',key: 'binding1', arguments:{'x-match':any,'a':'10'}},
{ queue:MYQUEUE ,exchange:'SECOND_EXCHANGE',key: 'binding2', arguments: {'x-match':any,'a':'10'}}]
> If so I would need to persist the "binding keys" (binding1, binding2) in order to remove
the bindings later.
> thanks for all your help,
> Matthew

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