gossip protocol
- Each node maintains a node membership list, which contains member IDs and heartbeat counters.
- Each node periodically increments its heartbeat counter.
- Each node periodically sends heartbeats to a set of random nodes, which in turn propagate to another set of nodes.
- Once nodes receive heartbeats, membership list is updated to the latest info.
- If the heartbeat has not increased for more than predefined periods, the member is considered as offline.
