Raft Consensus with a Minority of Nodes

A deep dive into modifying the Raft consensus protocol to use quorums based on finite projective planes instead of traditional majority quorums. By mapping cluster nodes to points in a projective plane, 'blocs' (lines) replace majority sets — any two blocs share exactly one node, preserving Raft's safety guarantee. The key benefit: consensus can be reached with far fewer nodes (e.g., 3 out of 7 instead of 4). The key trade-off: progress is not guaranteed whenever a majority is available — the active nodes must happen to form a valid bloc. The post walks through concrete scenarios with a 7-node Fano plane example, computes probabilities of a random active set containing a valid bloc, and discusses the Erdős–Ko–Rado theorem as a framework for understanding the design space. It also suggests topology-aware bloc design as a more practical alternative to pure combinatorial constructions.