Messages are not published directly to any specific message queue. Instead, the producer sends messages to an exchange. Exchanges are message routing agents, defined per virtual host within RabbitMQ. An exchange is responsible for the routing of the messages to the different queues. An exchange accepts messages from the producer application and routes them to message queues with the help of header attributes, bindings, and routing keys.
A binding is a link that you set up to bind a queue to an exchange.
The routing key is a message attribute. The exchange might look at this key when deciding how to route the message to queues (depending on exchange type).
Exchanges, connections, and queues can be configured with parameters such as durable, temporary, and auto delete upon creation. Durable exchanges will survive server restarts and will last until they are explicitly deleted. Temporary exchanges exist until RabbitMQ is shut down. Auto-deleted exchanges are removed once the last bound object is unbound from the exchange.
As we begin to explore more about messages, I want to give a big shoutout to Lovisa Johansson at CloudAMQP for permission to reprint information she and others have done an excellent job at obtaining. Everyone should visit CloudAMQP; it is an infinite source of wisdom when it comes to RabbitMQ.
