Backend & systems·Consistency and replication
a group of nodes has to agree on one value and keep agreeing even when some of them are unreachable or lying about the order.
Consensus
Also calledRaft, Paxos, distributed consensus
The protocol family that gets a majority of nodes to agree on an ordered sequence of decisions. It underpins leader election, configuration stores and distributed locks. It requires a majority to be reachable, so a three-node cluster survives one failure and a five-node cluster survives two — and an even number of nodes buys you nothing.