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From Fraser Adams <fraser.ad...@blueyonder.co.uk>
Subject Re: Messaging Flow Design in Qpid
Date Thu, 03 May 2012 17:30:52 GMT
On 02/05/12 19:54, m.luchak@smartasking.com wrote:
> , but even so I would be wary of implementing features that are not supported.
That's an interesting discussion/debate :-) I think Gordon Sim and I 
disagree on this one and he's more of the expert than I, however when we 
last discussed this topic (bad pun!!) he conceded that it might be 
useful to have a way to achieve intra (as opposed to inter) broker 
routing. I believe this too, so my assertion is that until a more 
appropriate mechanism is in place then a workaround using federation 
isn't so very bad.

The question about "supported" is interesting in the sense that the 
support of the qpid tools is variable, what I mean is that qpid-route 
has been around for a long time and works well, but has its limitations 
- for example federating using the headers exchange is limited to using 
queue routes (dynamic routes I believe work from qpid 0.12) but static 
routes don't - mainly because the command line options don't support it 
rather than because it can't be done by the broker. Similarly IIRC when 
you specify the exchange you use an exchange name, so (using the default 
exchanges) you couldn't federate between say a fan-out exchange to a 
headers exchange (though I'm pretty sure you can if you create your own 
exchanges of the same name but different type).

This isn't a criticism of qpid-route BTW so please don't take as such, 
it's merely a comment on the fact that it has grown relatively 
organically but doesn't necessarily do all of the federation 
possibilities that are available which may be useful, so I'm suggesting 
that support is a relative term.

All of this stuff *is* actually supported however because "under the 
hood" qpid-route used QMF methods to create links and bridges so if you 
construct what you need directly using QMF the broker will actually do 
it fine, which is why I believe my little hack of qpid-route is harmless 
- if I'd written my own little QMF application to do this stuff it'd be 
just another QMF application.

On your second question "Is there a simpler way to bind/unbind a queue 
to multiple exchanges? " your bindings *looked* OK (by eyeball - I 
haven't tried them). Unfortunately I'm not aware of a simpler/less 
verbose way to describe the bindings you want :-(

In UML terms I think that bindings would look like an association class 
between an exchange and a queue, so you you really have to specify both 
the exchange and the queue.

You've got me thinking though, it might have been nice to have a syntax 
such that one specifies an exchange & queue and a list of bindings 
between them. I suspect that a common use case might be multiple 
bindings between a given exchange and queue, so that way of describing 
things would be slightly less verbose. It's just an idle musing, there's 
probably a good reason that it's the way it is.

I use copy and paste reuse a lot when I'm creating addresses :-) It'd 
take me ages to put one together from scratch. I wish the documentation 
had some good headers exchange examples, I hate working things out from 


> 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?
> 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]
>> 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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