Peer-to-peer artifact distribution

Design a peer-to-peer file-transfer system (think a BitTorrent-style or WebRTC-datachannel-based distribution) for shipping large build artifacts (1–20 GB) to thousands of machines inside corporate networks, minimizing the load on a central origin. You need integrity guarantees, resumable transfers, and to work across NATs/firewalls. How do peers find each other, exchange chunks, and what's the central server still for?