Consensus protocols such as Raft allow a group to agree on a replicated log under specified failure assumptions. Majority quorums intersect, helping preserve committed decisions, but a partition without a quorum may be unable to make progress safely. Membership changes require protocol-specific procedures; changing a node list casually can break safety.

Gossip spreads membership or state information gradually. Anti-entropy compares replicas and repairs divergence; Merkle trees summarize ranges of data so replicas can locate mismatches without transferring every record. Repair consumes network and storage capacity and should not overwhelm foreground traffic.

Consensus does not make external side effects atomic. A leader-elected worker can become stale after a pause, so protected resources may need fencing tokens or idempotency. Use mature implementations and understand their operational assumptions instead of implementing a consensus protocol inside ordinary business code.