[rabbitmq-discuss] Naive Question

Sat Feb 11 01:53:44 GMT 2012

Hi Jerry,

Yeah, I think that makes sense.

Could your two queue be characterized like this:

1. Monitor creates the HB queue. With binding key "HB," consumer binds this queue to the exchange. Monitor writes to exchange with routing-key "HB."

2. Producer creates the MGMT queue. With binding key "MGMT," monitor binds this queue to exchange. Producer writes to exchange with routing-key "MGMT."

As always, thank you.

-Paul

On Feb 10, 2012, at 8:15 PM, "Jerry Kuch" <jerryk at vmware.com> wrote:

> Hi, Paul:
> 
> Nope:  Redeclarations of a queue with the same name and properties, within a
> vhost, are idempotent.  Redeclaring the thing before you start using it is
> a fairly common idiom.  If the resource didn't exist, then it's created;
> otherwise you've verified its existence.
> 
> Redeclaring a queue with a given name with different properties fails, so you
> can't accidentally vandalize some existing piece of messaging fabric that
> somebody else might be using.
> 
> On point b:  producers publish messages to *exchanges*, not to queues.
> Which queues, if any, the messages end up in depends on how queues
> are bound to the exchange in question, and the properties of the message.
> 
> With regard to your specific scenario with MGMT and HB messages, are you
> sure you want them in the same queue?  It's not really possible in any
> graceful way for a consumer to selectively read some but not other messages
> from a queue unless one does something obnoxious like basic.get-ing and then
> rejecting the messages you weren't interested in so that they're requeued.
> 
> From what I understand of the design you're sketching, you may want two
> queues, one from which the monitor reads MGMT messages and one from which 
> something else reads HB messages.  You could imagine binding both of those
> queues to a topic exchange and have your producer use routing keys to land
> your messages in the desired place.
> 
> Make sense?
> 
> Best regards,
> Jerry
> 
> ----- Original Message -----
> From: "Paul M. Bell" <pbell at syncsort.com>
> To: "RabbitMQ List" <rabbitmq-discuss at lists.rabbitmq.com>
> Sent: Friday, February 10, 2012 3:36:47 PM
> Subject: [rabbitmq-discuss] Naive Question
> 
> All,
> 
> Hi again.
> 
> Only after trying to think through a real world scenario did I realize that my grasp of certain fundamental AMQP concepts is tenuous.
> 
> Specifically, given a producer and a consumer, is the normative behavior for only *one* of them to declare (create?) the queue over which they communicate? As I look over the examples that I've "written" ("copied" would be more accurate), I see my producer doing this:
> 
> 
> RabbitAdmin admin = new RabbitAdmin(rabbitTemplate.getConnectionFactory());
> Exchange ex = new FanoutExchange(routingKey, true, false);
> admin.declareExchange(ex);
> admin.declareQueue(new Queue(this.queueName));
> 
> 
> And I see my consumer doing this:
> 
> 
> ConsumerSimpleMessageListenerContainer container = new ConsumerSimpleMessageListenerContainer();
> container.setConnectionFactory(connectionFactory());
> container.setQueueNames(this.queueName);
> container.setConcurrentConsumers(this.onOfConsumer);
> container.setMessageListener(new MessageListenerAdapter(new ConsumerHandler(), new SimpleMessageConverter()));
> container.startConsumers();
> 
> 
> What would happen if each declared a queue of the same name and type - would that give rise to two distinct queues, leaving the producer and consumer unable to communicate?
> 
> If it's normative for only one party to create the queue and the other to bind to it, what will happen if, when I try to bind to the queue, it doesn't yet exist?
> 
> Here's what I am trying to get to (I assume it requires a topic exchange):
> 
> a. a queue that holds two different message types, call them "MGMT" and "HB."
> b. a producer writes MGMT messages to this queue
> c. something called a "monitor" writes HB messages to this queue
> d. consumer reads HB messages from this queue
> e. monitor reads MGMT messages from this queue
> 
> Schematically I think it looks like this:
> 
> Producer(MGMT) -> monitor
> Monitor(HB)    -> consumer
> 
> How would I define these relationships via RabbitMQ? Who does what to whom?! I suspect it's simple, but after two solid weeks of 10 hour days, I am fried.
> 
> Thank you for your help.
> 
> -Paul
> 
> PS: What follows is not an attempt to curry favor - but this is a really fine list; folks are friendly, knowledgeable, and eager to help. I really appreciate it.
> 
> 
> 
> 
> 
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