This pattern is a more general form of the endpoint callback pattern. Here, a broker acts as an intermediary between the actual sender and recipients. Yes, multiple recipients can subscribe to a topic i.e. a named logical group of channels published by anyone.

In this case, the process of communication is as follows:

1. One or more listeners will inform a broker process that they are interested in subscribing to a topic
2. A publisher will post a message to the broker under the relevant topic
3. The broker dispatches the message to all the subscribers

A broker has the advantage of fully decoupling the sender and receiver in many senses. Additionally, the broker can perform many additional tasks, such as message enrichment, transformation, or filtering. This pattern is quite scalable and, hence, popular in enterprise middleware.

Celery internally uses publish/subscribe mechanisms for several of its backend transports, such as Redis for sending messages.