Design an online coding platform

Design an online coding practice and interview platform (similar to well-known coding challenge sites).

The platform should allow:

• Users to sign up, log in, and manage profiles.
• Users to browse, search, and filter coding problems.
• Users to write, run, and submit code solutions in multiple programming languages through a web-based editor.
• Automatic judging of submissions against hidden test cases, with results (e.g., Accepted, Wrong Answer, Time Limit Exceeded).
• Tracking of user statistics and progress (e.g., solved problems, difficulty distribution).

Requirements and considerations:

1. Functional requirements

• Problem management: create, update, and categorize coding problems (by difficulty, topic, etc.).
• Code execution: run user-submitted code safely and efficiently in isolated environments.
• Submissions: store submission history and results per user and per problem.
• Ranking/leaderboards: optionally show user rankings.

1. Non-functional requirements

• High availability and scalability to support millions of users and high QPS during peak times.
• Low latency for listing problems and fetching problem details.
• Reasonable turnaround time for judging submissions.
• Strong isolation and security for untrusted user code.

1. Constraints (assume)

• Target: 5M registered users, up to 200k daily active users.
• Peak: 10k code runs per minute.

Describe how you would design this system end-to-end. Talk about:

• High-level architecture and major components.
• Data modeling and storage choices.
• Code execution and sandboxing, including how to scale the judge/execution layer.
• Handling of traffic patterns, caching, and performance optimizations.
• Key trade-offs and how you would evolve the design as traffic grows.