System Design: Online Coding Practice and Judging Platform

Context

You are designing an online coding practice and judging platform similar to LeetCode/HackerRank/Codeforces. The platform must scale, be secure, and provide a great developer experience for both users and administrators.

Requirements

Design the end-to-end system with the following capabilities:

1. Core features

• User accounts, authentication, and roles (user, problem setter, admin).
• Problem browsing, filtering by tags/difficulty, and full‑text search.
• Multi-language submissions (e.g., C++, Java, Python, Go, JavaScript).
• Compilation and execution in sandboxed environments with resource limits.
• Distributed judge workers consuming jobs from a task queue.
• Result aggregation and storage of submission history, per‑test outcomes, and logs.

2. Data and lifecycle

• Test-data versioning: immutable test sets per version, problem versions, and mapping to submissions.
• Re‑judging: trigger re‑evaluation of submissions when test data or judging logic changes.

3. Platform safeguards

• Anti‑cheat and plagiarism detection.
• Rate limiting and fair‑use controls.
• Caching strategy for hot metadata, results, and artifacts.
• Observability: metrics, logs, tracing, and alerting.
• Security isolation: strong sandboxing, secrets management, and least privilege.

4. Deliverables

• High-level architecture and component responsibilities.
• APIs (major endpoints and request/response shapes, including streaming status if applicable).
• Data models (key entities and relationships) and storage choices.
• Execution pipeline for compilation and testing (including per‑language considerations).
• Scaling strategy (stateless vs stateful, sharding/partitioning, autoscaling).
• Failure handling and consistency model (queue semantics, retries, idempotency).

Assumptions: Make any reasonable scale assumptions (e.g., DAU, QPS, submissions/day) and state them explicitly. Call out trade-offs and alternatives when relevant.