Thus far, all message interaction in this book has been unidirectional, flowing from message publishers to consumers. What if a consumer wants to alert a publisher that processing is complete and send a reply, or a taxi driver wants to acknowledge a taxi booking request?

This chapter covers steps 5 to 10 in the taxi application system architecture, where a taxi driver responds to the customer and confirms a booking request. The taxi publishes its current location to a queue. The customer's application connects to the broker through WebSockets and subscribes to location updates, delivered directly from the taxi.

The Remote Procedure Call (RPC) request-response concept will be introduced, along with how to route a response back to the consumer. Since Advanced Message Queuing Protocol (AMQP) 0-9-1 , brokers provide four exchange types. This chapter also shows...