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From m.luc...@smartasking.com
Subject Re: Messaging Flow Design in Qpid
Date Wed, 02 May 2012 18:54:56 GMT

Thanks Fraser,
 
We are using the C++ broker - selectors working client side is  ok for us, but even so I would
be wary of implementing features that are not supported. That said, it seems a pretty harmless
hack and taking care not to create a binding loop would actually be trivial in our particular
case... so I guess I'll sleep on it ;)
 
Any insight on my second question?  Is there a simpler way to bind/unbind a queue to multiple
exchanges?
 
thanks again,
Matthew
 
-----Original Message-----
From: "Fraser Adams" <fraser.adams@blueyonder.co.uk>
Sent: Wednesday, May 2, 2012 2:36pm
To: users@qpid.apache.org
Subject: Re: Messaging Flow Design in Qpid



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) :-/

Frase



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
exchanges.
>
> 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]
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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