Start by clarifying requirements and scale (e.g., number of users, submissions per contest, language support), then design a high-level architecture with separate submission, compilation, and execution services. Focus on the critical components: sandboxed execution with resource limits, a scalable worker pool with priority queues for contests, and robust security measures. Discuss trade-offs like synchronous vs asynchronous processing and containerization vs VMs.
Pro tip: Emphasize the importance of idempotency and exactly-once processing for submissions, and how you would handle partial failures in the pipeline. Also, mention the need for a feedback loop to detect and mitigate new attack vectors in the sandbox.
Ask questions to understand expected load (e.g., submissions per second during contests), supported languages, and security requirements. Define functional and non-functional requirements.
Outline the main components: API gateway, submission service, compilation service, execution workers, result evaluator, and storage. Explain the flow from submission to verdict.
Detail how to isolate user code using containers or microVMs, enforce CPU/memory limits, and prevent network/file system access. Discuss time and memory limit enforcement.
Describe worker pool autoscaling, queue prioritization for contest submissions, and strategies to handle bursts (e.g., pre-warming workers, rate limiting).
Cover security measures like seccomp, AppArmor, and regular sandbox updates. Discuss monitoring, logging, and failure recovery to ensure reliability.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying requirements (scale, latency, consistency) and then walk through the write and read paths, emphasizing how comments are stored and ordered. Compare long polling, SSE, and WebSockets, and explain how you'd handle hot posts with high fan-out using a hybrid approach.
Pro tip: Demonstrate awareness of trade-offs by acknowledging that no single solution fits all scenarios; propose a hybrid approach (e.g., WebSockets for active users, long polling as fallback) and discuss how to handle hot posts with techniques like sharding and fan-out on write vs. read.
Ask about scale (DAU, comments per post), latency expectations (near real-time), consistency (eventual vs. strong), and moderation needs. This sets the stage for design decisions.
Outline how comments are written (API gateway, validation, moderation, storage) and read (fetching comments, ordering, pagination). Discuss data modeling (e.g., comment ID, post ID, timestamp, author) and storage choices (SQL vs. NoSQL).
Compare long polling, SSE, and WebSockets in terms of latency, overhead, scalability, and client support. Recommend a primary mechanism (e.g., WebSockets) with fallbacks.
Explain strategies for hot posts: sharding by post ID, fan-out on write vs. read, using a pub/sub system (e.g., Kafka, Redis Pub/Sub), and possibly rate limiting or batching updates.
Describe moderation pipeline (pre- or post-moderation, automated filters, human review) and how it affects real-time delivery. Explain comment ordering (chronological, threaded, ranked) and how to handle updates.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.