Message Broker

Introduction

A message broker is software that facilitates the exchange of messages between applications, systems, and services. It allows linked systems to communicate directly, even if they’re built using different technologies, deployed on separate platforms, or use distinct messaging protocols.
Message brokers promote async communications among services so that the sending app doesn’t have to wait for the receiving app's response. This improves fault tolerance and resiliency in the infrastructure.
Message brokers increase the flexibility to scale the applications

A service that responsible for transmitting messages. It's linked to the message broker, also known as publishers in the publish/subscribe model.

A service that receives messages waiting in the message broker. They’re known as subscribers in the publish-subscribe pattern.

Store the messages and send the messages with first-in first-out principle to consumer when consumer is active

a logical structure or an object that resides on queues and directs the message broker to form a group where consumers or producers can create or listen to send or receive messages.

A publisher can publish multiple topics
Topic can be published by multiple publisher and received by multiple subscriber
A subscriber can subscribe multiple topics

HTTP is a request-response protocol, it’s best used in synchronous communication, so the response must be waited before taking next action
Message brokers provide asynchronous communication between services. This means the producer doesn’t have to wait for a response from the receiving service. This increases the fault tolerance and robustness of systems.