Design a Peer-to-Peer File Sharing System (BitTorrent)

To design a BitTorrent-like system for a platform like Netflix, I would first focus on the core challenge: distributing massive video files efficiently across millions of devices without overloading central servers. The solution relies on three pillars: metadata management, peer discovery, and data transfer optimization. First, we generate a torrent file containing the file's hash tree, piece size, and initial tracker addresses. This allows clients to verify data integrity instantly. For peer discovery, instead of a single bottlenecked tracker, I'd propose a hybrid approach using a centralized bootstrap server for new nodes and a Distributed Hash Table (DHT) for decentralized lookup, ensuring high availability even if parts of the network fail. Next, the file is split into small chunks, typically 256KB to 4MB. Peers download these non-contiguous chunks from multiple sources simultaneously. To achieve speed and resilience, we implement a tit-for-tat algorithm where peers preferentially upload to those who upload back to them, preventing free-riders. We also use rarest-first piece selection to ensure all chunks remain available in the swarm. If a peer drops out, others seamlessly fill the gap. This architecture ensures that as demand grows, the aggregate bandwidth increases proportionally, making it ideal for Netflix's global content delivery needs.