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[ INFO ] category: System Design difficulty: hard freq: high first seen: 2026-01-12
[HARD][SYSTEM DESIGN][HIGH]data_engineeringwebWebSocketSystem DesignbackendMessage QueueReal-time Systems
$ cat problem.md
Design a live commenting system for YouTube live streams that supports real-time comment display, hot stream handling, and scalable architecture.
Requirements:
- Real-time comment display during live streams
- Support millions of concurrent viewers on popular streams
- Handle comment spikes during key moments
- Comment moderation and filtering
- Low latency delivery
Key Components:
- Comment Ingestion Service
- Message Queue (Kafka vs RabbitMQ discussion)
- WebSocket Gateway for real-time delivery
- Comment Storage (hot vs cold data)
- Rate Limiter
- Content Moderation Service
Discussion Points:
- Why Kafka over other message queues for high throughput?
- Handling hot streams with millions of viewers
- Fan-out strategies (per-viewer vs grouped connections)
- Comment ordering and consistency
- Spam and abuse detection