Membership Tracking

Each node maintains a list of cluster members + their state. Gossip exchanges include this list.

member_list = {
    "node1": {"address": "10.0.0.1", "state": "alive", "version": 5},
    "node2": {"address": "10.0.0.2", "state": "alive", "version": 4},
    "node3": {"address": "10.0.0.3", "state": "suspect", "version": 7},
}

When node A meets node B:

• Both share their member lists.
• Take the higher-version entry per node.
• Apply state transitions (alive → suspect → dead → leave).

States:

• alive: confirmed reachable recently.
• suspect: probe failed; not yet confirmed dead. Try to verify.
• dead: confirmed unreachable. Eventually removed.
• leaving: clean shutdown; replicate data before removal.

The version number ensures eventual convergence — older state is overridden by newer.

Initial bootstrap: a new node knows about ONE seed node. After joining, gossip teaches it about everyone else.

Hashicorp's Serf and HashiCorp Memberlist library implement this exactly. Used in Consul, Nomad.