Raft, made visible

Homonoia is an implementation of the Raft consensus algorithm, written from the paper and made visible in the browser. Five simulated nodes on a controllable network — you set latency, drop rate, duplication, partitions, and kill or revive nodes, then watch leader elections and log replication behave correctly under whatever you do to them.

The consensus core is pure: state in, state out, no I/O and no timers. The same code runs the visualization and the fuzz harness, so what you see on screen is the thing that was verified rather than a diagram of it. A 5,000-seed sweep covers 15M ticks, 41,879 leader changes, 447,766 entries committed and 9,974,273 messages sent, with no invariant violations.

Deleting a safety rule to check the tests catch it produced the more interesting result. With Raft’s commitment restriction removed, 5,000 seeds of random fuzzing found nothing — but a hand-written scenario fails at tick 1529. That class of bug isn’t reachable by fuzzing at all; you have to already know it exists and construct it.

TypeScript, React, 2D canvas. 128 tests.