System Design Mock Interview: Design Leetcode ft. Ex Google Engineer

Summary

Key Points

• Key non-functional requirements emphasize high availability, low latency for submission results, robust security and isolation for user-submitted code, and scalability to support millions of daily active users and 100,000 concurrent contest participants. 9:13
• DynamoDB, a NoSQL database, is chosen for storing problems and submissions due to its schema flexibility, lack of complex relational joins, and ability to handle nested data like test cases efficiently. 24:29
• The system design for LeadCode prioritizes core functional requirements including viewing coding problems, coding solutions in various languages, submitting solutions for instant feedback, and a live leaderboard for contests. 25:05
• User-submitted code will be executed in isolated containerized environments (e.g., Docker) to prevent security risks like malware or DDoS attacks and to optimize resource utilization compared to running directly on API servers or heavier VMs. 25:25
• API endpoints are designed to retrieve paginated and filtered lists of problems, fetch specific problem details by ID (with language filters), handle solution submissions, and provide real-time updates for the live contest leaderboard. 32:59
• The live leaderboard will utilize a submission schema indexed by competition ID for efficient querying and will implement a caching layer (like Redis) to reduce database load during high-traffic contest periods. 40:41
• To ensure scalability and manage traffic spikes, the system will employ horizontal scaling for runtime services and integrate a message queue between the API server and execution containers to smooth out job processing and enable retry mechanisms. 43:21
• Test cases for problems will be standardized across different programming languages, using serialization and deserialization mechanisms to adapt input and output formats for language-specific data structures. 44:38
• The submission database will implement a master-slave architecture to ensure fault tolerance and high availability, crucial for handling the high volume of contest submissions. 46:06