Decentralized cluster membership

Design cluster membership and failure detection for a fleet of 20,000 stateless service nodes spread across 8 regions, where every node needs a roughly-consistent view of which peers are alive (for client-side load balancing and gossip-based config). A central registry with heartbeats from 20k nodes is a hotspot and a single point of failure; you want a decentralized scheme. Address: how membership propagates without O(N^2) traffic, how you detect a dead node quickly without false-positive flapping during a brief network blip or a GC pause, and how you keep the membership view from oscillating (a flaky node repeatedly marked dead/alive) which would thrash all clients' load-balancing.