20 Pub/Sub Interview Questions and Answers

Publish/subscribe (or pub/sub) is a messaging pattern where senders of messages (publishers) do not specify receivers (subscribers). Instead, subscribers express interest in one or more classes of messages, and only receive messages that they are interested in. This can be useful in a number of situations, such as when messages are sent to a large number of recipients, or when the number of recipients is not known in advance.

If you’re interviewing for a position that involves pub/sub, you can expect to be asked questions about how the pattern works and what its benefits are. In this article, we’ll go over some of the most common pub/sub interview questions and how you can answer them.

Pub/Sub Interview Questions and Answers

Here are 20 commonly asked Pub/Sub interview questions and answers to prepare you for your interview:

1. What is Pub/Sub?

Pub/Sub stands for “publish/subscribe.” It is a messaging pattern that allows for loose coupling between applications. With Pub/Sub, applications can subscribe to certain topics, and then receive messages only for those topics. This allows for a more flexible architecture, as applications can come and go without affecting the overall system.

2. Can you explain the basic concepts and components of a publish-subscribe system?

In a publish-subscribe system, there are three main components: publishers, subscribers, and a broker. Publishers are the ones who generate the content that is to be shared, subscribers are the ones who want to receive that content, and the broker is the one who manages the distribution of the content.

The way it works is that publishers will send their content to the broker, and the broker will then distribute that content to all of the subscribers who have subscribed to that particular topic. This allows for a more efficient way of sharing information, as subscribers only receive the content that they are interested in, and publishers only need to send their content to one place.

3. What are some common use cases for Pub/Sub systems?

Some common use cases for Pub/Sub systems include social media applications, chat applications, and gaming applications.

4. How does Pub/Sub differ from traditional request-response approaches to communication?

In a traditional request-response approach, a client sends a request to a server and then waits for a response. With Pub/Sub, the client subscribes to a topic and then receives messages as they are published, without having to send a request. This can be useful when you want to receive updates in real-time, without having to constantly send requests.

5. Is it possible for multiple subscribers to receive messages published by a single publisher in Pub/Sub? If yes, then how do publishers control who receives their message?

Yes, it is possible for multiple subscribers to receive messages published by a single publisher in Pub/Sub. Publishers can control who receives their message by specifying the topic that the message should be published to. Subscribers can then subscribe to the appropriate topic in order to receive the message.

6. What’s your opinion on using Pub/Sub when there are only two parties involved?

I believe that Pub/Sub can be beneficial even when there are only two parties involved. It can help to decouple the components of your system and make it easier to scale. Additionally, it can help to improve performance by reducing the number of dependencies between components.

7. Why would anyone choose Polling over Event-Driven Pub/Sub Systems?

Polling is a simple and straightforward way to check for new data. It can be easily implemented and does not require a lot of infrastructure. Event-driven pub/sub systems are more complex and can be more difficult to set up and maintain. However, they are more efficient and can scale better to handle large amounts of data.

8. What are some advantages of Pub/Sub over other architectural styles like RPC or REST?

Pub/Sub has a few advantages over other architectural styles. First, it allows for decoupling of components, so that components can communicate without needing to know about each other. Second, it can improve performance by reducing the number of messages that need to be sent. Finally, it can provide a more scalable solution since messages can be sent to multiple subscribers at once.

9. What is an event bus?

An event bus is a software architecture pattern that allows for loose coupling between software components by providing a central place for them to communicate. This communication is typically in the form of events, which can be emitted by one component and then received and handled by another. Event buses can be used to decouple components in a variety of different ways, making them very flexible.

10. What is the difference between topics and queues in Pub/Sub?

Topics are used for one-to-many communication, where messages are broadcast to all subscribers of the topic. Queues are used for one-to-one communication, where each message is delivered to a single subscriber.

11. What happens if no subscriber is available at the time of publishing?

If there are no subscribers available when a message is published, then the message will be lost.

12. Can you give me some examples of use cases where a Pub/Sub architecture works well?

Pub/Sub is a great way to handle communication between different parts of a system where there are a lot of messages being sent and received. It can be used for things like chat applications, news feeds, or any other system where there are a lot of messages being exchanged.

13. Can you explain what asynchronous messaging is?

Asynchronous messaging is a method of communication between two or more parties in which the messages are not sent or received at the same time. This type of messaging can be useful when the parties are not able to communicate in real-time, or when the message sender does not need an immediate response from the message receiver.

14. What is the difference between synchronous and asychronous messaging models?

The synchronous messaging model is a one-to-one model where each message is sent from one sender to one receiver. The asynchronous messaging model is a one-to-many model where each message can be sent to multiple receivers.

15. What happens if a message fails to be delivered to one of its intended recipients?

If a message fails to be delivered to one of its intended recipients, then it will be placed in a dead letter queue. The message will remain in the dead letter queue until it is either delivered to the intended recipient or it expires.

16. What are durable and non-durable subscriptions?

A durable subscription is one where the messages are stored by the message broker until they are consumed, even if the consumer is not active at the time the message is published. A non-durable subscription is one where messages are only stored until they are consumed or until the message broker restarts, at which point they are lost.

17. Can you explain what dequeuing means in context with Pub/Sub?

Dequeuing is the process of removing messages from a queue. In the context of Pub/Sub, this would refer to removing messages from the message queue that have been published by the publisher and are awaiting processing by the subscriber.

18. What is Pub/Sub used for in cloud computing scenarios?

Pub/Sub is a messaging pattern that is often used in cloud computing scenarios. It allows for communication between different parts of a system, or between different systems, in a decoupled way. This means that each part of the system can subscribe to the messages that it is interested in, and does not need to be aware of the other parts of the system.

19. How can you ensure that messages published through Pub/Sub are received by all subscribers?

There are a few ways to ensure that messages published through Pub/Sub are received by all subscribers. One way is to use a message queue, which will hold onto messages until all subscribers have received them. Another way is to use a fan-out exchange, which will send a copy of the message to all subscribers.

20. Which companies use Pub/Sub to power their products or services?

Google, Amazon, and Facebook are all companies that use Pub/Sub to power their products or services.