Interview Questions Bank

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Overview

This is a curated list of system design interview questions organized by difficulty and topic. Use this to practice and assess your readiness.

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Question Bank by Difficulty

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🟢 Easy (Entry Level / New Grad)

These questions test basic concepts and don’t require complex distributed systems knowledge.

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🟡 Medium (Mid-Level / 2-5 YOE)

These questions require understanding of distributed systems, caching, and scalability.

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🔴 Hard (Senior / Staff Level)

These questions require deep expertise and consideration of complex trade-offs.

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Questions by Topic

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Data-Intensive Applications

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Real-Time Systems

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Social & Content Platforms

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Location & Mapping

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E-Commerce & Transactions

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Sample Interview Questions with Hints

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Question 1: Design a URL Shortener

Requirements to clarify

• How many URLs per day? (100M writes, 10B reads)
• How long should URLs be valid? (configurable, default forever)
• Custom short URLs allowed?
• Analytics needed?

Key design points

1. Encoding: Base62 encoding (a-z, A-Z, 0-9)
2. ID Generation: Counter + Base62 or random hash
3. Storage: Simple key-value (Redis) + persistent DB
4. Caching: Cache popular URLs in Redis
5. Database: NoSQL (DynamoDB) works well

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Question 2: Design Twitter Timeline

Requirements to clarify

• Active users? (300M DAU)
• Tweet rate? (500M tweets/day)
• Follow limits? (5000 following)
• Celebrity accounts? (millions of followers)

Key design points

1. Fan-out on write: Pre-compute timelines for most users
2. Fan-out on read: For celebrities (too many followers)
3. Hybrid approach: Write to cache for most, read-time merge for celebrities
4. Caching: Redis sorted sets for timelines
5. Ranking: Chronological + engagement signals

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Question 3: Design WhatsApp

Requirements to clarify

• Users? (2B users, 100M DAU)
• Message rate? (100B messages/day)
• Group size? (1024 members max)
• Message types? (text, image, video)

Key design points

1. Connection: WebSocket for real-time
2. Message flow: Sender → Server → Recipient (or queue if offline)
3. Group messages: Fan-out on server
4. Delivery status: Sent → Delivered → Read
5. Offline handling: Queue messages, deliver on reconnect

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Question 4: Design Netflix

Requirements to clarify

• Users? (200M subscribers)
• Content size? (10K titles, petabytes of video)
• Concurrent streams? (10M peak)
• Quality levels? (480p to 4K)

Key design points

1. Video processing: Transcode to multiple qualities
2. Streaming: HLS/DASH adaptive bitrate
3. CDN: Multi-tier CDN, edge caching
4. Recommendations: ML-based personalization
5. Search: Elasticsearch for content discovery

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Question 5: Design Uber

Requirements to clarify

• Users? (100M riders, 5M drivers)
• Rides/day? (20M)
• Location update frequency? (every 4 seconds)
• Matching criteria?

Key design points

1. Location tracking: Redis GEO or QuadTree
2. Matching: Scoring algorithm (distance, rating, ETA)
3. Real-time: WebSocket for location updates
4. Pricing: Dynamic pricing based on supply/demand
5. Trip state: State machine (requested → matched → in-progress → completed)

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Self-Assessment Checklist

Before your interview, make sure you can:

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Fundamentals

• Calculate QPS, storage, and bandwidth requirements
• Choose between SQL and NoSQL with justification
• Explain CAP theorem and when to prioritize what
• Design a basic caching strategy
• Draw a load-balanced architecture

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Intermediate

• Design for horizontal scalability
• Implement consistent hashing
• Choose between push vs pull models
• Design for fault tolerance
• Handle data partitioning/sharding

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Advanced

• Design for global scale (multi-region)
• Handle distributed transactions
• Implement exactly-once delivery
• Design real-time systems
• Handle hot partitions

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Practice Schedule

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Week 1-2: Foundation

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Week 3-4: Core Systems

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Week 5-6: Advanced Systems

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Week 7+: Mock Interviews

• Do 2-3 mock interviews per week
• Time yourself (45 minutes)
• Practice with a friend or use Pramp/Interviewing.io
• Record yourself and review

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Resources for Each Question

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Free Resources

• System Design Primer (GitHub)
• High Scalability Blog
• Company Engineering Blogs
• YouTube: Gaurav Sen, Tech Dummies, System Design Interview

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Paid Resources

• “Designing Data-Intensive Applications” (Book)
• “System Design Interview” by Alex Xu (Book)
• Educative.io System Design Course
• ByteByteGo Newsletter