What are the most common system design questions?

Here are some of the most common system design questions that frequently appear in interviews for software engineering roles, particularly at companies like Google, Amazon, Facebook, and other tech firms. These questions often cover popular applications and services, focusing on scalable and reliable architecture.

1. Design a URL Shortener (e.g., TinyURL)

• Purpose: Convert long URLs into short, easy-to-share links and redirect users from short URLs to the original.
• Key Components: URL mapping, hash generation, database design, caching, and handling redirects.
• Challenges: Unique URL generation, high read/write traffic, and URL expiration.

2. Design a Social Media Feed (e.g., Twitter Timeline or Facebook Newsfeed)

• Purpose: Display a user’s feed with posts from friends or people they follow.
• Key Components: Timeline generation, database design, caching, and efficient retrieval of recent posts.
• Challenges: Real-time updates, efficient sorting, caching strategies, and handling high-traffic loads.

3. Design a Chat System (e.g., WhatsApp or Facebook Messenger)

• Purpose: Enable real-time messaging between users, both one-on-one and in groups.
• Key Components: Message storage, delivery mechanisms, message queues, database design, and load balancing.
• Challenges: Real-time message delivery, read receipts, offline messaging, and group chat management.

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

• Purpose: Stream video content to users with minimal latency.
• Key Components: Video storage, content delivery network (CDN), video encoding, caching, and load balancing.
• Challenges: Scalability, efficient video storage and retrieval, adaptive bitrate streaming, and managing high concurrent loads.

5. Design an E-Commerce Platform (e.g., Amazon)

• Purpose: Create a platform where users can browse products, add items to a cart, and make purchases.
• Key Components: Product catalog, user accounts, shopping cart, order management, payment processing, and recommendation systems.
• Challenges: Inventory management, user authentication, payment processing security, scalability, and handling large product catalogs.

6. Design a Search Engine (e.g., Google)

• Purpose: Enable users to search for content across the internet or within a specific site.
• Key Components: Crawling, indexing, ranking algorithms, and query processing.
• Challenges: Efficiently crawling and indexing massive amounts of data, ranking results, and handling frequent queries.

7. Design a File Storage System (e.g., Dropbox or Google Drive)

• Purpose: Allow users to upload, store, and share files.
• Key Components: File storage, metadata storage, access control, file retrieval, and content delivery.
• Challenges: Managing storage and retrieval efficiency, handling versioning, access permissions, and scalability for large file sizes.

8. Design a Load Balancer

• Purpose: Distribute incoming requests across multiple servers to ensure reliability and performance.
• Key Components: Request routing, health checks, load balancing algorithms (e.g., round-robin, least connections), and failover mechanisms.
• Challenges: Ensuring high availability, managing failure detection and recovery, and choosing appropriate routing strategies.

9. Design a Notification System (e.g., for Facebook or Instagram)

• Purpose: Send notifications to users about events, such as new messages, friend requests, or likes.
• Key Components: Event processing, notification delivery mechanisms, user preferences, and batch processing.
• Challenges: Real-time and batch notifications, managing user preferences, ensuring timely delivery, and scaling for millions of users.

10. Design a Ride-Sharing Service (e.g., Uber or Lyft)

• Purpose: Connect riders with drivers in real-time, track rides, and facilitate payments.
• Key Components: Real-time location tracking, driver-rider matching, pricing algorithms, and ride history.
• Challenges: Real-time tracking and matching, handling dynamic pricing, managing a large user base, and ensuring data accuracy.

11. Design a Payment System (e.g., PayPal or Stripe)

• Purpose: Process transactions securely between payers and payees.
• Key Components: Payment gateways, authentication, fraud detection, transaction history, and user accounts.
• Challenges: Ensuring security and fraud prevention, handling high volumes of transactions, and complying with financial regulations.

12. Design a Content Delivery Network (CDN)

• Purpose: Cache and deliver content close to users to reduce latency and improve load times.
• Key Components: Caching, edge servers, load balancing, and data replication.
• Challenges: Reducing latency, optimizing cache invalidation, handling high traffic, and ensuring global availability.

13. Design a Rate Limiter

• Purpose: Limit the number of requests a user can make to a system to prevent abuse.
• Key Components: Request counters, time-based limits, IP tracking, and error handling.
• Challenges: Handling burst traffic, ensuring fair distribution, and designing a scalable rate-limiting algorithm.

14. Design an Online Polling/Voting System

• Purpose: Create a platform where users can cast votes or participate in polls.
• Key Components: User authentication, vote recording, vote tallying, and data integrity.
• Challenges: Ensuring vote accuracy, preventing multiple votes from the same user, handling high loads, and ensuring real-time updates.

15. Design a Job Scheduling System (e.g., for background tasks or cron jobs)

• Purpose: Schedule and manage background tasks that run at specific intervals or on specific triggers.
• Key Components: Task queues, workers, scheduling algorithms, and monitoring.
• Challenges: Task prioritization, ensuring fault tolerance, monitoring task status, and handling delayed or failed tasks.

Additional Tips for Common System Design Questions

1. Understand the Requirements: For each problem, identify and clarify both functional and non-functional requirements, such as scalability, availability, and latency.
2. Use a Structured Approach: Follow a clear structure—define requirements, outline high-level architecture, detail individual components, address scalability, and discuss trade-offs.
3. Prepare for Follow-Up Questions: Interviewers may ask for details about specific components, scaling strategies, or trade-offs you’ve made in your design.
4. Know Your Trade-Offs: Be prepared to explain the advantages and limitations of each decision, such as consistency vs. availability, performance vs. cost, and complexity vs. simplicity.
5. Practice Real-World Scenarios: Many of these questions are inspired by real applications, so studying how actual systems like Twitter, Netflix, or Uber work can provide valuable insights.

System design questions are open-ended and often require a high-level solution rather than specific code. Familiarizing yourself with these common questions and practicing a structured approach can help you confidently tackle system design interviews.