First, Understand the 'Why'
Before diving into specific prompts, it's crucial to understand what interviewers are really looking for. A system design interview isn't a test of memorization; it's an evaluation of your thought process. The interviewer gives you a broad, open-ended
prompt like "Design Instagram" to see how you handle ambiguity, make trade-offs, and architect a solution that is scalable, reliable, and maintainable. They want to see you clarify requirements, sketch a high-level architecture, and then dive into the details of specific components, all while communicating your reasoning clearly. Mastering this framework is more important than knowing the 'perfect' answer to any single question.
1. The Social Feed
Prompts like "Design Twitter/X," "Design a Facebook News Feed," or "Design Instagram" are classics for a reason. They are designed to test your understanding of systems that handle a massive volume of reads and a high volume of writes. The core challenge is designing a feed generation service. How do you efficiently deliver a personalized feed to millions of users in real-time? This involves thinking about data modeling (SQL vs. NoSQL), caching strategies to reduce latency, and the trade-offs between pushing updates to users versus pulling them on demand. You'll need to discuss how to handle the 'fan-out' problem, where a celebrity's post needs to be delivered to millions of followers.
2. The Content and Media Platform
This category includes prompts like "Design YouTube," "Design Netflix," or "Design a file-sharing service like Google Drive." Here, the focus shifts to handling large binary objects—videos, images, or files. Your interviewer will want to hear you discuss the use of a Content Delivery Network (CDN) to serve content quickly to a global user base. You'll also need to consider how to handle uploads, including breaking large files into smaller chunks, and designing a robust storage system, likely using object storage like Amazon S3. Key concepts to touch on include video transcoding, metadata management, and API design for uploading and downloading content.
3. The Real-Time Service
Prompts such as "Design a ride-sharing app like Uber/Ola" or "Design a food delivery service like Zomato" fall into this bucket. These questions test your ability to design systems that manage real-time data and location-based services. The core challenge is continuously updating the locations of many users (drivers) and efficiently matching them with other users (riders). You'll need to discuss using technologies like WebSockets for real-time communication, geospatial indexing for fast location-based queries, and the architecture of the matching service that lies at the heart of the system. Scalability and low latency are critical here.
4. The Foundational Utility
This group includes deceptively simple prompts like "Design a URL shortener like TinyURL," "Design a rate limiter," or "Design Pastebin." While they seem smaller in scope, they are perfect for assessing your grasp of core distributed systems concepts. For a URL shortener, you'll need to discuss how to generate a unique, short ID, how to handle the mapping between short and long URLs at scale, and the design of a highly available redirection service. A rate limiter prompt tests your knowledge of algorithms (like token bucket or leaky bucket) and how to implement them in a distributed environment to protect your services from overload.
5. The E-Commerce Engine
Designing a platform like Amazon or Flipkart, or even a smaller component like a movie ticketing system, tests a different set of skills. These systems are transactional and require high consistency. You'll need to talk about how you would design services for product catalogs, user shopping carts, order management, and payment processing. This is a chance to discuss database choices that ensure ACID compliance for transactions, strategies for managing inventory to prevent overselling, and the importance of reliability and security, especially when handling payments. The search and recommendation engine is also a common deep-dive topic within this category.
