I started with the streaming pipeline and spent probably too long on ingest and CDN before getting to the interactive bits, which is really the interesting part of the question.
Start by clarifying the scale, latency requirements, and key interactive features (polls, reactions, Q&A) to scope the design. Then propose a high-level architecture that separates the live video streaming pipeline from the real-time interaction layer, using WebSockets or similar for low-latency updates. Finally, dive into trade-offs around consistency, scalability, and cost, and discuss how to measure success with product metrics.
Pro tip: Emphasize the importance of graceful degradation: during peak load, prioritize core streaming and basic interactions over non-critical features to maintain user experience. Also, highlight how you would instrument the system to gather real-time engagement metrics for product iteration.
Ask questions to understand expected concurrent viewers, latency targets, types of interactive features, and platform constraints (e.g., mobile, web). Define success metrics like engagement rate and poll response time.
Outline components: video ingestion and delivery (CDN, transcoding), real-time interaction service (WebSocket servers, pub/sub), and data stores for polls and user responses. Explain how they integrate.
Detail the design for polls: how to broadcast questions, collect responses, aggregate results, and display them with low latency. Discuss consistency models (e.g., eventual vs. strong) and trade-offs.
Address scaling to millions of concurrent users: horizontal scaling of WebSocket servers, load balancing, sharding, and failover. Discuss how to handle spikes and ensure high availability.
Discuss trade-offs between latency, consistency, cost, and complexity. Explain how to prioritize features and measure impact, and how the design supports future interactive features.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.