Choosing Between Queues and Topics: Deciding the Right Communication Pattern for Your System

Introduction

In software projects, we often encounter queues and topics, two different ways of setting up communication channels between system components. It can be challenging to know when to use one over the other, so let's explore the differences and use cases for each.

The problem

Imagine you’ve got two components in your system that need to talk to each other. Maybe one part is producing/creating data and the other part needs to consume/fetch it. How do you set up a smooth communication channel between them? This is where queues and topics come into play.

note: I assume we want asynchronous communication between our components.

Queues And Topics

What is a Queue?

Think of a queue like a line at a coffee shop. Customers (messages) wait in line, and the barista (receiver) serves them one by one. Each message is delivered to and processed in a queue by a single receiver.

What is a Topic?

Now, imagine you’re at a concert. The band (producer) plays music, and everyone in the audience (consumers) hears it. A topic works like this, messages are broadcast to all subscribers.

Is Queue == Single Consumer Topic?

You may think that queues are just topics with only one consumer, but that’s not entirely true.

The main difference between a queue and a topic in a distributed system is that the producer in the queue (barista) knows exactly who is receiving the message, while in a concert, the band has no idea who is listening to their music.

Real-World Examples of Queues and Topics

Understanding how queues and topics work in theory is one thing, but seeing how they are applied in real-world scenarios can make the concepts even clearer.

Queues in Action

1. Order Processing in E-commerce
   In an online store, customer orders are placed into a queue. This ensures each order is processed in the order it was received, preventing duplicates and missed orders.
2. Email Sending Services
   When sending a large volume of emails, each email is placed in a queue. The system sends out the emails one by one, efficiently managing the load and ensuring no emails are lost.
3. Video Encoding
   When uploading videos to a platform, they need to be encoded into different formats. These platforms use queues to manage encoding jobs, ensuring each video is processed in order and efficiently.

Topics in Action

1. Notification Systems in Social Media
   When you post an update, it is published on a topic. All your friends subscribed to this topic receive the update almost instantly, ensuring everyone sees it at the same time.
2. Stock Price Updates on Trading Platforms
   Trading platforms use topics to broadcast stock price changes. When a stock price changes, the update is published to a topic, and all subscribed interfaces receive it simultaneously, keeping everyone informed.
3. Live Sports Updates
   Sports apps use topics to broadcast live match updates. When a goal is scored, the update is published to a topic, and all users following the match are notified immediately, providing a real-time experience for fans.

Technologies

Let me show you some tools that can help with your specific needs. You should check them out and choose the best one for your situation.

• Apache Kafka
• RabbitMQ
• Apache ActiveMQ
• Amazon Simple Queue Service (SQS)

Conclusion

Queues and topics are essential for managing and distributing information. Queues are ideal for tasks requiring ordered, single-consumer processing, while topics excel in broadcasting messages to multiple consumers in real time.

I hope you enjoyed :))