Why is the gossip protocol critical to ScyllaDB's cluster membership?

In a large peer-to-peer cluster with no central coordinator for membership, every node needs a way to learn which other nodes exist, whether they're alive, and their basic state (load, schema version, token ownership) without a single point of failure or a central registry becoming a bottleneck. Gossip solves this by having each node periodically exchange state with a few random peers, and that state naturally propagates across the whole cluster within a few rounds, exponentially fast, similar to how a rumor spreads through a social network.

Because gossip is decentralized and doesn't rely on any single node staying up, cluster membership information keeps propagating correctly even while individual nodes fail or restart, which is essential for a system with no master node coordinating everything centrally. ScyllaDB still uses gossip for liveness/failure detection and general cluster state today, even though schema and topology changes themselves have moved to Raft for strong consistency - the two mechanisms serve different needs: gossip for scalable, resilient state dissemination, Raft for operations that must never be ambiguous.