To consume a rabbitmq queue, do I really need to declare the exchange and the queue?

Question

In all the examples I find online, I see the exchange and the queue being declared before a messages are consumed. Declaring the exchange seems weird, because, why would I do it? I'm consuming a queue, which might be bound to multiple exchanges (or to none, maybe it just have old messages waiting in it).

also, I can't think of why I would declare a queue. This will require me to know information about the queue that I don't need to know to consume it (like auto_delete and durability).

When I tested it locally, I can consume a queue without declaring anything. It works. So I'm left wondering, why does every example I've seen online, declare the exchange and queue, even if it just consumes it?

thanks!!!

Blah

Answer 1

"All" the example you saw are self contained. And they trying to give you a working example. Because in case you don't have all the components setted up, your example will fail.

In terms of "why I would declare a queue". The real-life example is when your consumer wants to consume messages that are relevant with the current configuration. In this case it will create an exclusive ( no one else can connect to this queue ) and will start consume messages.

Back to your answer. No you don't need to do this. You can pre-create exchange, binding and queue ahead of time and then just pass the names to the code.

Athanasia

Answer 2

In general, you don’t need declare exchange and queue in consumer. You must assemble "exchanges/queues" topology somewhere else. It's like schema in database.

But always there are exceptions. When you need "private" queue (exclusive=true) for real-time processing, consumer must know (by configuration) about source exchange and bind own queue to it.

In other case i can imagine situations where publisher declare exchange and consumers can discover it using some convention (pattern) for exchange naming.

Futtock