Which system design interview questions are asked most frequently, and what key topics do they cover?

System design interviews put candidates in the architect’s seat, asking them to design complex systems on the fly. The most frequently asked questions tend to involve designing well-known applications – think chat services, social media feeds, or URL shorteners. Each one touches on core system architecture concepts. These questions cover topics like scalable systems design, data storage (SQL vs NoSQL databases), caching layers, load balancing, and real-time data processing. Understanding these high-level design topics will help you tackle any question with confidence.

Most Common System Design Interview Questions (and What They Cover)

Below are some of the system design interview questions candidates face most often, along with the key topics they encompass:

1. Design a Chat Application (e.g. WhatsApp or Messenger)

Real-time communication services are a favorite interview question. Key topics include:

• Real-time messaging protocols: Using WebSockets or long polling to achieve low-latency, two-way message delivery.
• Scalable infrastructure: Designing servers and message queues to handle millions of concurrent users (horizontal scaling, load balancing).
• Data storage & synchronization: Storing chat history across devices, using databases for messages and ensuring data sync across multiple devices.
• Reliability: Ensuring message delivery with acknowledgments and retries, and considering end-to-end encryption for security.

2. Design a URL Shortener (e.g. TinyURL)

This is a classic system design question for entry-level interviews. Key topics include:

• Unique ID generation: Creating short, unique keys (using base-62 encoding or hashing) and avoiding collisions when generating new short URLs.
• Database design: Storing mappings from short URL to original URL efficiently, and choosing between SQL vs NoSQL for quick lookups.
• High read throughput: Optimizing for a high volume of redirects (reads) per second using caching and replication.
• Scalability & expiration: Partitioning data (sharding) as the number of URLs grows, and handling features like URL expiration or custom aliases.

3. Design a Social Media Feed (e.g. Twitter or Instagram)

Social network design questions test your ability to handle large-scale traffic and personalized feeds. Key topics include:

• News feed generation: Aggregating posts from friends/followed accounts, and ranking content using algorithms (e.g. based on recency or engagement).
• Data modeling: Designing databases to store user profiles, relationships (followers), posts, likes, and comments. Often involves a combination of relational and NoSQL stores.
• Caching and content delivery: Using caches (like Redis) and CDNs for images/videos to serve feed content quickly to users globally.
• Scalability: Handling read-heavy traffic (many users fetching feeds) and write-heavy events (many posting simultaneously) by horizontal scaling, load balancing, and efficient database queries.

4. Design an E-commerce System (e.g. Online Store like Amazon)

E-commerce platforms combine multiple components and often come up in interviews. Key topics include:

• Microservices architecture: Separating the system into services (product catalog, user accounts, shopping cart, order processing, payment) for maintainability and scalability.
• Database transactions: Ensuring inventory counts and orders remain consistent using transactions or distributed locking (especially during checkout and payment).
• Search and recommendation: Implementing product search (possibly with text indexing) and personalized recommendations (using user behavior data).
• Scalable systems: Handling high traffic during peak times (like sales events) by auto-scaling, load balancing, and caching frequently viewed product data.

5. Design a Video Streaming Service (e.g. YouTube or Netflix)

Video platforms test your ability to handle large media files and high bandwidth. Key topics include:

• Content storage & CDN: Storing video files reliably and using Content Delivery Networks to stream videos with minimal latency to users worldwide.
• Video encoding and quality: Handling video upload, transcoding into various resolutions/bitrates, and supporting adaptive streaming (adjusting quality to user’s bandwidth).
• Recommendation engine: Providing personalized content suggestions based on user watch history (involves big data and possibly machine learning components).
• High throughput streaming: Designing for many simultaneous viewers, using load balancers and distributed servers to serve video segments without buffering.

6. Design a Search Engine or Web Crawler

This is a complex question often reserved for senior candidates. Key topics include:

• Web crawling: Building a crawler to systematically fetch pages from the web. Consider politeness, avoiding overload on websites, and breadth-first vs depth-first crawling strategies.
• Indexing: Creating an inverted index mapping keywords to documents (web pages) so searches can be answered quickly. This involves efficient data structures and possibly distributed storage (like Elasticsearch or Solr).
• Query handling: Designing the query service that handles user search queries, finds relevant pages from the index, and ranks results (basic ranking algorithms).
• Scalability: Distributing the crawl and index across multiple servers, handling updates (new or changed pages), and ensuring the system can handle many search queries per second.

Other common system design questions include ride-sharing services (like Uber), file storage platforms (like Dropbox), and notification systems. For more examples and detailed answers, see our Top 10 System Design Interview Questions and Answers article, or browse the complete list in our System Design Interview Questions guide. For advanced or less common challenges, refer to our 50 Advanced System Design Interview Questions compilation.

Key System Design Topics and Concepts

No matter the question, certain technical interview tips hold true. System design problems consistently require knowledge of core topics in system architecture:

• Scalability & Load Balancing: Know how to scale out with horizontal scaling vs. vertical scaling, and use load balancers to distribute traffic evenly.
• Data Storage: Understand when to use SQL vs. NoSQL databases, how to do sharding (partitioning) and replication for large datasets, and when caching is appropriate to reduce database load.
• Caching & CDN: Explain how caching (in-memory stores like Redis) improves performance and how CDNs cache static content closer to users to reduce latency.
• Consistency & Availability: Be ready to discuss trade-offs (CAP theorem) – for instance, when to favor eventual consistency over strong consistency in a distributed system.
• High Availability & Fault Tolerance: Discuss designing systems with redundancy (multiple servers, data replicas) so that a single failure won’t cause downtime.
• Security & Reliability: Touch on securing user data (encryption, authentication) and ensuring reliable communication (retries, acknowledgements, idempotency in APIs).

Understanding these concepts will allow you to adapt to any system design scenario thrown at you. Interviewers often dive into these fundamentals while discussing your solution.

Check out the 10 must-do system design interview questions.

Tips for Acing a System Design Interview

Designing a system on the spot can be daunting, but a structured approach will showcase your skills effectively. Here are some best practices and technical interview tips to help you shine:

1. Clarify requirements: Begin by asking clarifying questions about scope and requirements. This shows you think about high-level design goals (e.g. should the system prioritize consistency or availability? real-time updates or batch processing?).
2. Outline the high-level architecture: Draw or describe a big-picture solution first – major components like clients, servers, databases, load balancers, etc. Starting with a clear overview of the system architecture helps the interviewer follow your thought process.
3. Discuss components and trade-offs: Break the problem down into core subsystems (such as database design, caching, messaging queue, etc.). For each, explain your choices and alternatives. Mention trade-offs (like SQL vs NoSQL, or monolith vs microservices) and why your design fits the problem.
4. Consider scalability and bottlenecks: Explain how your design handles a growing number of users or data (using techniques like sharding, replication, caching). Identify potential bottlenecks and how to mitigate them, demonstrating you can design scalable systems.
5. Mind reliability and security: Include thoughts on fault tolerance (e.g. multiple servers across data centers) and security measures (encryption, authentication, rate limiting) in your design. This shows you can build robust, production-ready systems.
6. Communicate clearly: Throughout the interview, talk through your reasoning. Use simple language and analogies if needed (remember the target is around an 8th-grade reading level for clarity). An authoritative yet conversational tone helps convey confidence without arrogance.
7. Practice with mock interviews: Finally, engage in mock interview practice. Simulate the interview setting with a friend or use online platforms to practice system design questions. This helps you get comfortable articulating your thoughts within a time limit and handling feedback or hints.

By following these tips, you’ll demonstrate both your design thinking and your communication skills – a winning combination for system design interviews.

Conclusion

In summary, the system design interview questions asked most frequently revolve around designing popular, large-scale applications and understanding core architectural topics like scalability, data management, and performance. By familiarizing yourself with these common scenarios and the principles behind them, you’ll be well-equipped to handle variations of these questions. Remember to articulate your thought process clearly and cover the key considerations we discussed – this demonstrates a methodical approach to system design.

Ready to take your system design skills to the next level? Join our community at DesignGurus.io and enroll in courses like Grokking the System Design Interview. You’ll get a structured curriculum, real-world examples, and expert guidance (plus plenty of practice problems) to help you ace your next interview. Sign up today and start building the confidence to design systems that scale!

FAQs

Q1: What are system design interviews and why are they important? A system design interview is a discussion where you’re asked to design a software system or architecture. It’s important because it tests your ability to create scalable, efficient systems and evaluate trade-offs. Companies use it to gauge your design skills, problem-solving approach, and how well you understand system architecture in real-world scenarios.

Q2: How can I prepare for a system design interview? Reviewing the basics of scalable system design – databases, caching, load balancing, etc. Practice common system design questions (like those mentioned above) and study their solutions from resources or courses (our Grokking the System Design Interview course is a great resource). Sketch out designs on paper or a whiteboard. Also, do mock interviews to simulate the real thing and get feedback.

Q3: What are some common system design interview questions I should practice? Frequently asked examples include designing a URL shortener, a chat application, a social media news feed, an e-commerce site, or a video streaming service. These cover a range of topics like real-time messaging, scalable systems design, database management, and more. By practicing these, you’ll cover many fundamentals needed for other design problems too.

Q4: How is a system design interview different from a coding interview? In a coding interview, you write code to solve algorithmic problems, focusing on correctness and efficiency. In contrast, a system design interview is about the high-level architecture of a large system. There’s usually no coding; instead, you’ll outline components, data flow, and decisions for building a complex, scalable system. This format tests your big-picture thinking.

Q5: How detailed should I get in a system design interview? Aim for a balanced high-level design with just enough detail. Start with the broad architecture (clients, servers, databases, etc.), then drill down into a few critical components. Explain your key decisions and assumptions, but avoid needless low-level details – focus on choices that impact scalability and reliability.