🍻 Pub Sub 🍻

A terrible pun intended ☝️

Have you ever joined a mailing list or followed an account on social media? Have you ever subscribed to a channel on YouTube?

If your answer is "Yes!" to any of the questions above then congrats! 🎉 You pub-subbed.

Pub-subbed [ 📢 puhb-suhbd ]
⚪ verb
Becoming a part of publish-subscribe messaging system.
Creating a publish-subscribe messaging system.
"He pub-subbed his way out of the problem."

Mailboxes — More accurate image to represent pub/sub

What is pub/sub?

Pub/sub in its full form publish/subscribe is a messaging pattern. It is a way for different components of a system to notify each other and it's a great alternative to polling.

In this pattern there are - you guessed it - publishers📤 and subscribers📥. In addition to them there are messages✉️ and channels/topics 📫.

💯 Publishers can have any amount of subscribers
🕵️‍♂️ Publishers don't have to know about their subscribers
⬅️ Publishers send messages to channels or topics to which subscribers can subscribe

💯 Subscribers can subscribe to any amount of publishers
🕵️‍♂️ Subscribers don’t need to know who the message comes from
➡️ Subscribers receive messages from channels or topics to which publishers send messages

What are the advantages of pub/sub?

✅ Decoupling/Loose coupling

Since neither the publishers nor the subscribers have to know about each other pub-subbing helps with the decoupling of system components.

✅ Scalability

When number of subscribers or channels/topics increases adding new servers to the system helps with dealing with the increased load.

✅ Asynchronicity

Since publisher sends its messages to a channel or topic it doesn't have to wait for a subscriber to receive the message. And since the subscriber receives messages from a channel/topic it doesn't have to wait for a message. In fact it doesn't have to be up when the message was sent.

Do all these remind you something? Hint: The answer is a design pattern.

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The answer is: Observer!

Pubsub is similar to Observer design pattern of Gof 🙆‍♂️.

🔒 Which problems does Observer solve? 🔒

From Gof

How can a one-to-many dependency between objects be defined without making the objects tightly coupled?
How can an object notify an open-ended number of other objects?

🔑 How does Observer solve these problems? 🔑

From Gof

Define Subject and Observer objects
- Subject -> Publisher and channel/topic
- Observer -> Subscriber
When a subject changes state, all registered observers are notified and updated automatically
- Subject changes state -> Publisher sends a message to channel/topic
- Observers are notified and updated -> Subscribers are notified and updated

Similarities

Just like in pubsub, in observer the subjects don't have to know about their observers and vice versa.
Just like in pubsub, in observer the subjects can have any amount of observers and vice versa.
Just like in pubsub, subjects and observers are loosely coupled.
Just like in pubsub, observers can be updated asynchronously.

If you're not sick of me associating things, both observer pattern and pub/sub messaging reminds me of the mailing systems in human world 🤷‍♂️. It's really cool to see concepts from computing world resemble human world 💻 🌎.