System design: HLD interview questions

Preparing for high-level design (HLD) interviews involves a deep understanding of system architecture, scalability, and real-world problem-solving. Here are 100 HLD interview questions you can use to prepare:

System Design Basics

1. How would you design a URL shortening service like TinyURL?
2. Design a parking lot system.
3. How would you design an online book reader system like Kindle?
4. Design an ATM machine.
5. How would you design a rate-limiting system for an API?
6. Design a distributed file storage service like Google Drive.
7. How would you design a video streaming service like YouTube?
8. Design a scalable notification system.
9. How would you design a search autocomplete system?
10. Design a logging and monitoring system for a distributed service.
11. How would you design a chat system like WhatsApp?
12. Design an e-commerce website like Amazon.
13. How would you design a recommendation system like Netflix?
14. Design a news feed system like Facebook’s.
15. How would you design a social media platform like Twitter?
16. Design a system to schedule jobs (e.g., cron job scheduler).
17. How would you design a web crawler?
18. Design a ride-sharing system like Uber.
19. How would you design a scalable ticket-booking system?
20. Design a notification system for social media.
21. How would you design a scalable document editor like Google Docs?
22. Design an image hosting service like Imgur.
23. How would you design a payment gateway like Stripe?
24. Design a file transfer system like Dropbox.
25. How would you design a multiplayer online game server?
26. Design a location-based search service like Google Maps.
27. How would you design a content delivery network (CDN)?
28. Design a scalable messaging queue system like Kafka.
29. How would you design an email service like Gmail?
30. Design a blogging platform like Medium.
31. How would you design a notification delivery service?
32. Design a cloud-based photo album system.
33. How would you design a scalable customer support ticketing system?
34. Design a key-value store like Redis.
35. How would you design a high-throughput analytics platform?

Scalability and Performance

1. How would you scale a service to handle millions of users?
2. How would you design a load balancer?
3. How would you handle rate-limiting in a distributed system?
4. How would you design a system to handle high-traffic spikes (e.g., flash sales)?
5. How would you design a system to handle millions of file uploads simultaneously?
6. How would you design a scalable metrics and monitoring system?
7. How would you reduce latency in a global system with users from different regions?
8. How would you scale a distributed system with minimal downtime?
9. How would you design a system for consistent hashing?
10. How would you implement horizontal scaling in a database?
11. How would you design a caching system for high-traffic websites?
12. How would you design a rate limiter to handle burst traffic efficiently?
13. How would you design a data replication system across multiple data centres?
14. How would you design a high-availability service?
15. How would you design a system to ensure eventual consistency in a distributed environment?

Security and Privacy

1. How would you design a system to authenticate millions of users securely?
2. How would you handle user session management in a distributed system?
3. How would you implement data encryption for sensitive data in a system?
4. How would you design a secure API gateway?
5. How would you handle data privacy in a distributed system?
6. How would you secure user data in a high-traffic service?
7. How would you design a system to prevent DDoS attacks?
8. How would you design a system with secure access control and permissions?
9. How would you implement secure communication between microservices?
10. How would you design a system to detect and prevent fraud?

Database Design

1. How would you design a system to handle millions of database transactions?
2. How would you design a scalable NoSQL database?
3. How would you design a system to store and manage large-scale time-series data?
4. How would you design a distributed database with high availability?
5. How would you design a system with both SQL and NoSQL databases?
6. How would you design a database sharding strategy for scalability?
7. How would you implement data partitioning in a distributed database system?
8. How would you handle schema migrations in a high-availability system?
9. How would you design a system for multi-region database replication?
10. How would you design a distributed database with ACID properties?

Real-Time Systems

1. How would you design a real-time chat application?
2. How would you design a real-time bidding system like Google Ads?
3. How would you design a real-time leaderboard for a gaming platform?
4. How would you design a real-time event streaming system?
5. How would you design a real-time collaboration tool like Figma?
6. How would you design a real-time traffic monitoring system?
7. How would you design a real-time stock trading platform?
8. How would you design a real-time fraud detection system?
9. How would you design a real-time sports analytics system?
10. How would you design a real-time vehicle tracking system?

Microservices and APIs

1. How would you design a microservices architecture for a large-scale system?
2. How would you design an API rate-limiting solution?
3. How would you design an API gateway for microservices?
4. How would you design a service discovery mechanism in a microservices architecture?
5. How would you design an inter-service communication system for microservices?
6. How would you design a microservices system to ensure backward compatibility?
7. How would you design a distributed tracing system for microservices?
8. How would you design a data consistency mechanism across microservices?
9. How would you implement version control for APIs in a large system?
10. How would you handle circuit-breaking in a microservices architecture?

Miscellaneous

1. How would you design a distributed transaction system?
2. How would you design a notification delivery service using webhooks?
3. How would you design a system to handle billions of write requests per second?
4. How would you design a system for video transcoding at scale?
5. How would you design a service for personalized advertisements?
6. How would you design a system to manage a large number of IoT devices?
7. How would you design a system for real-time data analytics on streaming data?
8. How would you design a document version control system like Git?
9. How would you design a content moderation system for a social platform?
10. How would you design a system for machine learning model deployment and serving?

These questions cover various aspects of system design, ranging from scalability to performance, database architecture, and real-time systems.