RabbitMQ is a message broker software used as an intermediary between different applications or services to communicate with each other. One application/service sends messages to the queue and another application/ service receives messages from the queue. To understand RabbitMQ properly, we need to be familiar with the following topics,

• Message: The data being sent from one application/service to another. It could be any information such as notifications, commands, objects etc.
• Queue: Queue stores messages from the producers and keeps them until consumers receive the messages or expire.
• Producer: Producer produces or sends a message to the queue.
• Consumer: Consumer consumes or receives messages from the queue.
• Exchange: Producer sends messages to the exchange and the exchange sends those messages to one or more queues based on its routing rule.
• Binding: Binding is a rule that links each exchange to a queue.

In RabbitMQ, exchanges are responsible for routing messages to queues based on certain criteria. There are several types of exchanges, each with its own routing behaviour. Here are the main types of exchanges:

1. Direct Exchange: Direct exchange sends messages to the queues with the same binding key as the messages routing key. For example, if binding key of a queue is something.1.1, then the direct exchange will send message to that queue if the routing key of that message is exactly something.1.1.
2. Topic Exchange: Topic exchange doesn't have to match the routing key with the binding key, instead it follows a wildcard pattern. For that, the routing key can have two special characters, * and # to match exactly one word and zero to more than one word accordingly. For example, For example, 'animal.*' matches 'animal.bird', not 'animal.bird.owl'. Again 'animal.#' matches 'animal' or 'animal.bird' or 'animal.bird.owl'.
3. Fanout Exchange: Fanout exchange sends the message to all bounded queues without considering the routing key.
4. Headers Exchange: Headers Exchange sends messages to the queues based on the header of messages and queues rather than the routing key.
5. Default Exchange: It is a special exchange without any name. It routes messages to the queue using the queue name as the routing key. That means Default exchange routes messages to the queues having the name same as the routing key of those messages.

This spring boot complete project is about communication between producer and consumer, using four kinds of exchange ( topic exchange, direct exchange, fanout exchange and header exchange ).

Scenario: The system has lots of students and few instructors. Each student can subscribe to multiple instructors. Instructors can send notice to his students or a particular student or even all students.

Design: I've tried to use four kinds of exchange here.

• Direct Exchange: I used direct exchange while sending notices to individual students.
• Topic Exchange: While sending a notice to his subscribers.
• Fanout Exchange: To send notices to all students.
• Headers Exchange: While sending notifications to students having the same headers key value, I named it sending notices to secure channel.