Introduction
Messaging patterns are essential in software development, and Pub-Sub Messaging is one such popular messaging pattern. The pub-sub messaging pattern allows decoupling between software components, enabling communication between them without any direct dependencies.
This pattern is particularly useful in distributed systems where components may be spread across different physical locations. In this article, we will explore the concept of Pub-Sub Messaging, its use cases, and how it is implemented.
What is Pub-Sub Messaging?
Pub-Sub stands for Publisher-Subscriber, which is a messaging pattern that facilitates the exchange of messages between multiple components without creating direct dependencies between them.
In this pattern, publishers publish messages on topics, and subscribers subscribe to topics to receive the messages. The publishers and subscribers are decoupled from each other, and they interact through a message broker.
When a publisher publishes a message on a topic, the message broker receives the message and sends it to all the subscribers that have subscribed to the topic. Subscribers receive the messages without knowing the publisher’s identity, and publishers are unaware of the subscribers’ identities.
This pattern ensures that the publishers and subscribers do not have any direct dependencies on each other.
Architectural Components in Pub-Sub Messaging
Publishers
Publishers are entities responsible for generating messages and sending them to the messaging system. They publish these messages without the need to know who, if anyone, will receive them.
Publishers simply publish messages to specific topics or channels, without any direct knowledge of the subscribers.
Subscribers
Subscribers are entities that express interest in specific topics or channels and receive messages accordingly. They register with the messaging system to listen for messages that match their interests.
When a message is published to a topic that a subscriber is subscribed to, the messaging system delivers the message to the subscriber.
Message Broker
The Message Broker acts as an intermediary between publishers and subscribers. It receives messages from publishers and distributes them to interested subscribers based on their subscriptions.
The broker handles the routing and delivery of messages, ensuring that subscribers only receive the messages they are interested in.
Topics (Channels)
Topics are logical channels that categorize messages based on their content. Publishers send messages to specific topics, and subscribers subscribe to the topics they are interested in.
This allows for a scalable and organized way to handle various types of messages within the messaging system.
Message Queue
In some Pub-Sub messaging systems, a message queue may be used to temporarily store messages until they are delivered to subscribers.
This helps to decouple the publishers from the subscribers, ensuring that messages are not lost if a subscriber is temporarily unavailable.
Message Filtering
Message filtering mechanisms may be employed to allow subscribers to receive only a subset of messages within a topic. This can be based on specific criteria defined by the subscriber, such as message attributes or content.
Use-cases
Pub-Sub Messaging is used in various real-world scenarios, including:
Social Media
Social media platforms use Pub-Sub Messaging to notify users of new messages, notifications, and updates.
The platform’s backend publishes the notifications on specific topics, and the user’s clients subscribe to these topics to receive the updates.
Financial Services
In the financial sector, Pub-Sub Messaging is used to disseminate real-time data feeds, such as stock prices and market news.
The data is published on topics, and the subscribers, such as traders and analysts, receive the data in real-time without any direct dependencies.
Internet of Things (IoT)
In the IoT world, Pub-Sub Messaging is used to connect various devices and sensors.
Devices publish data on specific topics, and other devices or cloud services subscribe to these topics to receive the data.
Conclusion
Pub-Sub Messaging is a powerful messaging pattern that enables decoupling between software components, facilitating effective communication between them.
Many microservice systems rely on some form of Pub-sub messaging usually to decouple their internal systems and this is one skill one should try to learn about.