This one has more surface area than it looks.
Start by clarifying the scope and requirements of Facebook Live commenting, such as scale, real-time delivery, and moderation needs. Then design the core APIs for posting, retrieving, and moderating comments, focusing on trade-offs between consistency, latency, and scalability. Finally, discuss how the APIs integrate with Facebook's existing infrastructure and handle edge cases like high traffic and spam.
Pro tip: Emphasize idempotency and rate limiting in your API design to prevent duplicate comments and abuse, showing you understand production challenges. Also, mention how you would leverage Facebook's existing systems (e.g., Graph API, Thrift) to avoid reinventing the wheel.
Ask questions to understand the scale (e.g., millions of concurrent viewers), latency requirements (real-time vs. eventual consistency), and features (replies, reactions, moderation). This ensures your design meets actual needs.
Outline the essential endpoints: POST /live/{video_id}/comments for posting, GET /live/{video_id}/comments for retrieval (with pagination), and DELETE /comments/{comment_id} for deletion. Specify request/response schemas and status codes.
Discuss how comments are pushed to viewers in real-time, using WebSockets or long polling. Explain the trade-offs between push and pull models and how to handle ordering and delivery guarantees.
Describe strategies for scaling, such as sharding by video ID, caching, and using a message queue for asynchronous processing. Mention idempotency keys and rate limiting to ensure reliability.
Explain how to integrate moderation APIs (e.g., for spam detection, profanity filtering) and authentication/authorization (e.g., OAuth tokens). Consider privacy and data retention policies.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.