System Design Interview Prep: Must-Know Questions

System design interviews. They can feel like climbing Mount Everest without a map. I remember my first one. I walked in confident, only to be bombarded with questions I wasn't prepared for. I stumbled, I sweated, and I definitely didn't get the job. But I learned a lot.

Today, I'm going to share the must-know system design questions that, if you prepare for them, will drastically increase your chances of landing that dream role. We'll break down the types of questions, how to approach them, and what interviewers are really looking for.

Why System Design Matters

Before we dive in, let's address the elephant in the room: why do companies even care about system design? It's simple. They want to know if you can:

Think big picture.
Design scalable systems.
Understand trade-offs.
Communicate effectively.

These skills are critical for any senior engineer or architect.

Types of System Design Questions

System design questions aren't all created equal. They generally fall into a few broad categories:

Scalability: How do you design a system to handle millions of users?
Performance: How do you optimize a system for speed and low latency?
Availability: How do you ensure a system stays up and running even when things fail?
Consistency: How do you maintain data integrity across a distributed system?

Let's look at some specific questions in each category.

Must-Know System Design Questions

Scalability Questions

Design a URL Shortener (like TinyURL)
- Focus: Hashing, load balancing, database design.
- Key Considerations: Collision handling, unique ID generation, scalability of the storage layer.
Design a Rate Limiter
- Focus: Algorithm selection (token bucket, leaky bucket), distributed counters.
- Key Considerations: Preventing abuse, handling bursts of traffic, scalability of the counter system.
Design a Social Media Feed
- Focus: Fan-out on write vs. fan-out on read, caching strategies, database sharding.
- Key Considerations: Real-time updates, personalized feeds, handling large numbers of followers.

Performance Questions

Design a Caching System
- Focus: Cache eviction policies (LRU, LFU), cache consistency, distributed caching.
- Key Considerations: Minimizing latency, handling cache misses, scalability of the cache cluster.
Design a Search Autocomplete System
- Focus: Trie data structure, ranking algorithms, caching of popular searches.
- Key Considerations: Low latency, relevant suggestions, handling misspellings.

Availability Questions

Design a Distributed Key-Value Store
- Focus: Consistent hashing, replication strategies, fault tolerance.
- Key Considerations: Data consistency, handling node failures, scalability of the storage layer.
Design a Message Queue (like RabbitMQ or Amazon MQ)
- Focus: Message durability, at-least-once vs. at-most-once delivery, message ordering.
- Key Considerations: Handling message loss, ensuring message delivery, scalability of the queue system.

Consistency Questions

Design a Distributed Transaction System
- Focus: Two-phase commit, Paxos/Raft consensus algorithms, handling conflicts.
- Key Considerations: Data consistency, atomicity, durability.
Design a system for Movie Ticket Booking (like BookMyShow)
- Focus: Concurrency control, optimistic locking, handling seat reservations.
- Key Considerations: Preventing double-booking, ensuring seat availability, scalability of the reservation system.

General Design Questions

Design an E-commerce Platform (like Flipkart)
- Focus: Microservices architecture, database design, caching strategies, payment processing, order management, scalability, security, and user experience.
- Key Considerations: High availability, fault tolerance, data consistency, and integration with third-party services.

How to Approach System Design Questions

Now that you know the types of questions, let's talk about how to approach them. Here's a framework I've found helpful:

Clarify Requirements: Ask clarifying questions to understand the scope and constraints.
Outline High-Level Design: Sketch out the major components and their interactions.
Deep Dive into Key Components: Focus on the most challenging aspects of the system.
Discuss Trade-offs: Explain the pros and cons of different design choices.
Consider Scalability and Performance: Think about how the system will handle growth and high load.
Address Failure Scenarios: Discuss how the system will handle failures and maintain availability.

Example: Let's say you're asked to design a URL shortener.

Clarify: How many URLs will be shortened per day? What's the expected read/write ratio? Do we need analytics?

High-Level: User enters a long URL -> System generates a short URL -> System stores the mapping -> User accesses short URL -> System redirects to the long URL.

Deep Dive: Hashing algorithm for generating short URLs, database schema for storing mappings, caching strategy for popular URLs.

Trade-offs: Using a shorter URL vs. reducing the chance of collisions, using a relational database vs. a NoSQL database.

Scalability: Load balancing across multiple servers, sharding the database.

Failure: Handling database failures, replicating data across multiple regions.

What Interviewers Are Looking For

It's not just about getting the "right" answer. Interviewers want to see:

Problem-Solving Skills: Can you break down a complex problem into smaller, manageable pieces?
Technical Depth: Do you understand the underlying technologies and concepts?
Communication Skills: Can you explain your ideas clearly and concisely?
Design Sense: Do you have a good intuition for what makes a system well-designed?

They want to see how you think, not just what you know.

Where Coudo AI Comes In (A Sneak Peek)

Want to put your system design skills to the test? Check out Coudo AI, the LLD learning platform.

Here at Coudo AI, you find a range of problems like snake-and-ladders or expense-sharing-application-splitwise to test your knowledge in a practical setting.

FAQs

Q: How much detail should I go into during a system design interview?

That depends on the time you have and the interviewer's interest. Start with a high-level overview and then dive deeper into the most important aspects. Don't get bogged down in unnecessary details.

Q: What if I don't know the answer to a question?

Be honest and explain your thought process. It's better to show how you would approach the problem than to try to bluff your way through it.

Q: How important is it to draw diagrams during a system design interview?

Very important. Diagrams can help you communicate your ideas more clearly and concisely. They also show the interviewer that you can think visually.

Closing Thoughts

System design interviews are challenging, but they're also a great opportunity to showcase your skills and knowledge. By preparing for these must-know questions and practicing your approach, you'll be well on your way to landing that dream job. And remember, it's not just about the answer, it's about the journey. So, embrace the challenge, learn from your mistakes, and keep pushing forward. If you are looking to practice real-world problems, try Coudo AI problems now.