Definition
Pub/Sub, or publish subscribe, is a messaging pattern where senders of messages, called publishers, do not broadcast messages directly to specific receivers, called subscribers. Instead, publishers categorize messages into classes without knowledge of which subscribers, if any, exist. Subscribers express interest in one or more classes and receive only the messages that are of interest, without knowledge of publishers. This decoupling allows for asynchronous communication and scalability, making systems more resilient and adaptable. For instance, an e-commerce application might use Pub/Sub to notify various services like inventory management, shipping, and customer notifications when a new order is placed. This differs from direct point-to-point messaging where a sender must know the specific recipient. Pub/Sub concepts are frequently assessed in cloud security certifications like CCSP and AWS exams.