Raft in a Storm — Break a Five-Node Cluster Without Breaking Safety
Partition leaders, crash replicas, strand writes without a quorum, and then watch higher-term AppendEntries reconcile every stale suffix while three continuously measured safety invariants stay intact.
What this is
A deterministic, five-node Raft-style cluster you can operate and sabotage from one browser tab. Pause on any 100 ms boundary, submit client commands, crash and restart durable replicas, or activate any of the ten links to cut it. Terms, roles, election countdowns, votes, AppendEntries, acknowledgements, log conflicts, commit indexes, and quorum receipts are all live simulator state.
The one-click storm is a reproducible protocol story: a leader is stranded with one follower, accepts a write it cannot commit, a three-node majority elects a newer leader, that side temporarily loses its own quorum, and the cluster finally heals. The stale suffix disappears. The committed prefix does not.
Why this is mind-blowing
Most consensus diagrams animate circles and ask you to trust the caption. This one keeps evidence. Every elected term has a leader ledger. Every commit has the exact replica set that proved its majority. Every committed slot is fingerprinted so a rollback or conflicting value would stop the clock immediately. During a partition the logs may honestly diverge; after healing, the convergence instrument measures when all live logs and commit indexes become identical again.
That turns Raft's promise from “the arrows looked right” into something falsifiable: break availability as aggressively as you want, then inspect why safety survived.
Prompt
Build “Raft in a Storm — Break a Five-Node Cluster Without Breaking Safety,” a polished single-file browser simulation of a five-node Raft-style cluster. Visualize terms, roles, election timers, AppendEntries/votes in flight, each node’s replicated log and commit index. Let users pause/step/play, submit commands, crash/restart nodes, partition/heal links, and trigger a deterministic “storm” preset. Preserve the core safety behaviors: at most one elected leader per term in the simulator, majority required for commit, logs reconcile after healing, and committed entries never roll back. Surface measurable invariants and a live event trace rather than merely animating dots. Include reset, deterministic seed, keyboard/pointer/touch controls, responsive 390px layout, accessible labels/focus, and reduced-motion behavior. One self-contained HTML file, inline CSS/JS, no dependencies/assets/CDN/fetch/network/build; <=160KB.Paste into your favorite AI and adapt it to your context.
What I learned shipping it
- A leader can accept a client command while isolated, but the command is not committed until acknowledgements prove the entry exists on at least three of five durable logs.
- A newly elected leader's current-term barrier forces stale uncommitted suffixes to meet a conflicting entry after healing, so reconciliation is visible without ever rewriting a committed slot.
- Consensus animation becomes an engineering tool only when election uniqueness, quorum evidence, committed-prefix fingerprints, message drops, and convergence time are exposed as inspectable measurements.