Thanks for the reply Gordon , so another question that I had regarding the
same topic was about the hello world example and how it is functioning ? In
that example , we have a message producer and a consumer the producer sends
a message to the default topic exchange amq.topic . Now I am confused with
the example primarily because of two reasons:
1-A message is being sent to a default Topic Exchange however no queue has
been associated with it ? Dont topic exchanges have topic queues
2-What is the routing key of the message being sent ? since there is no
subject in the message isnt the routing key empty ?

I would appreciate it if you could help me understand that.


On Thu, Dec 1, 2016 at 7:52 PM, Gordon Sim <g...@redhat.com> wrote:

> On 01/12/16 18:46, James Franco wrote:
>
>> I am trying to wrap my head around the association of topics and queues
>> with an exchange. Here is my understanding so far (please correct me if I
>> am wrong). In the end I have a question .
>>
>> Point 1:
>> Whenever we create a queue by default it is under the default exchange
>> amq.direct.We can move this queue to a different direct exchange using the
>> bind command shown below:
>>
>> ./qpid-config bind NameOfDirectExchange NameOfQueue bindingKey
>>
>> Now I would like to know more about topics. Whenever we create a topic we
>> use the command resembling the one below
>>
>> ./qpid-config add exchange topic news
>>
>> Now the above command is basically creating an exchange of topic type.
>>
>> My question is how can I create a topic without creating a new exchange  ?
>> Say if I wanted to create a topic under the default exchange amq.topic?
>>
>> Is it possible for one exchange to have both topics and queues ? I would
>> think not because an exchnage can be either Direct , topic , fanout or
>> headers am I correct ?
>>
>
> In AMQP 0-10 and earlier, messages are always published to an exchange and
> always consumed from queues.
>
> Exchanges have bindings associated with them. These are just rules on
> which queues the exchange should forward (or route) a given message to.
>
> There are different types of exchange. The exchange type dictates what
> form the binding 'rules' can take. For a fanout exchange, a binding to a
> queue means that all messages to that exchange should go to that queue. For
> a direct exchange, each binding specifies a 'key' that is matched against a
> special property (called a routing key) of the message being routed using
> an exact match; messages whose routing key is exactly the same as the key
> of a binding are routed to the queue that binding is associated with. A
> topic exchange also uses a key in its bindings, but the matching allows for
> wildcards.
>
> The 'topic' exchange type is (in my view) an unfortunate choice of name.
> You can achieve JMS style 'topic' semantics using any of the exchange
> types. The difference is whether you need wildcard matching or not.
>
> A queue can be bound to more than one exchange, and there can be more than
> one binding between a given queue and exchange (providing these bindings
> differ in some way, e.g. have a different key). Binding doesn't move a
> queue in any way.
>
> The 'default exchange' is really just a way to give the illusion of being
> able to send direct to a queue. The bindings of the default exchange are
> guaranteed to route a message whose routing key is the queue name to that
> queue (and only that queue).
>
> Hope this helps a little. There are some better explanations of the
> concepts available [1][2][3]. Note though that these concepts are specific
> to pre 1.0 versions of the AMQP protocol.
>
> [1] http://qpid.apache.org/releases/qpid-java-6.1.0/java-broker/
> book/Java-Broker-Concepts-Exchanges.html
> [2] https://www.rabbitmq.com/tutorials/amqp-concepts.html
> [3] https://access.redhat.com/documentation/en-US/Red_Hat_Enterp
> rise_MRG/1.1/html/Messaging_User_Guide/chap-Messaging_
> User_Guide-Exchanges.html
>
>
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