Anycast edge routing system
Design an anycast edge routing system where the same set of IP prefixes is advertised via BGP from 200 PoPs worldwide, so each user's packets land at the topologically nearest PoP. It must absorb volumetric DDoS at the edge, fail a PoP out of rotation within seconds (withdraw its routes) when it's unhealthy or overloaded, and avoid breaking long-lived TCP/TLS sessions when BGP re-converges and a user's flow suddenly lands on a different PoP. Constraints: 100M+ requests/sec aggregate, no single PoP becomes a hotspot. Walk through the routing/control model, the failover mechanism, and the central trade-off.
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.