Pub/sub pattern in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Pub/Sub pattern in system design?

The Pub/Sub (Publish/Subscribe) pattern is a messaging model where senders (publishers) send messages without knowing who will receive them, and receivers (subscribers) listen for messages on topics they are interested in. It decouples message producers from consumers.

intermediate

How does the Pub/Sub pattern improve system scalability?

By decoupling publishers and subscribers, the system can add more subscribers or publishers independently. Messages are distributed asynchronously, allowing components to scale without waiting for each other.

beginner

What role does a message broker play in the Pub/Sub pattern?

A message broker acts as an intermediary that receives messages from publishers and routes them to the appropriate subscribers based on topics or channels.

intermediate

Name two common challenges when implementing Pub/Sub systems.

1. Ensuring message delivery guarantees (like at-least-once or exactly-once). 2. Handling message ordering and duplicates.

beginner

Give a real-life example that illustrates the Pub/Sub pattern.

Think of a newspaper subscription: The newspaper company (publisher) prints news and sends it out. Subscribers receive newspapers based on their subscription topics without the company knowing each reader personally.

In the Pub/Sub pattern, who decides which subscribers get the messages?

A The message broker based on topics

B The publisher directly

C The subscriber sends a request

D The network router

The message broker routes messages to subscribers based on the topics they subscribe to.

What is a key benefit of using Pub/Sub over direct messaging?

A Tight coupling between components

B Synchronous communication

C Decoupling of message producers and consumers

D Guaranteed message order

Pub/Sub decouples producers and consumers, allowing them to operate independently.

Which component typically stores and forwards messages in a Pub/Sub system?

A Publisher

B Subscriber

C Message broker

D Load balancer

The message broker intermediates message delivery between publishers and subscribers.

What problem might occur if message ordering is not handled in Pub/Sub?

A Messages may be lost

B Subscribers may receive messages out of order

C Publishers get blocked

D Subscribers cannot subscribe

Without ordering, subscribers might process messages in the wrong sequence.

Which of these is NOT a typical use case for Pub/Sub?

A Event notification systems

B Real-time chat applications

C Direct database queries

D Log aggregation

Direct database queries are not a Pub/Sub use case; Pub/Sub is for asynchronous messaging.

Explain the Pub/Sub pattern and how it helps in building scalable systems.

Think about how publishers and subscribers communicate without knowing each other.

Describe common challenges faced when implementing a Pub/Sub system and possible solutions.

Consider what can go wrong when messages are sent asynchronously.