Jepsen Test

Run Jepsen-Style Cluster Tests

Validate correctness of the deployed gossip-rs system using real network behavior. This complements in-process deterministic simulation testing (DST) by testing the actual binary with real (or simulated-real) networking.

Evidence Base

Key insight: DST and Jepsen are complementary, not competing. DST explores the state space exhaustively in-process with a simulated network. Jepsen validates the real deployed system with real networking and OS behavior.

When to Use

• After implementing a gossip protocol and wanting to verify convergence
• Before releases to validate coordination correctness under real conditions
• When DST passes but you suspect real networking reveals different bugs
• When testing integration between components (not just protocol logic)

When NOT to Use

• When the gossip protocol doesn't exist yet (use /sim-scaffold first)
• For testing pure state machine logic (use /sim-run instead — faster, deterministic)
• For testing detection engine correctness (no distributed aspect)

Two Modes

Mode A: Maelstrom (Lightweight, Development-Time)

Tests the gossip protocol in isolation using Maelstrom's simulated network. Fast iteration, no infrastructure needed.

Mode B: Full Jepsen (Heavyweight, Pre-Release)

Tests the full deployed system with real SSH, real binaries, real network partitions. Thorough but slow and potentially flaky.

Default to Mode A unless the user specifically requests Mode B or the change involves integration between multiple deployed components.

Mode A: Maelstrom

Prerequisites

1. Maelstrom binary installed (brew install maelstrom or from jepsen-io/maelstrom releases)
2. A Maelstrom-compatible binary wrapper exists at crates/gossip-worker/src/bin/maelstrom_gossip.rs
3. The gossip protocol implements the sans-IO pattern (from /sim-scaffold Type B)

If the Maelstrom binary wrapper doesn't exist, guide creation:

// crates/gossip-worker/src/bin/maelstrom_gossip.rs
//
// Thin wrapper that adapts the sans-IO GossipProtocol to Maelstrom's
// JSON stdin/stdout protocol.
//
// Reads Maelstrom JSON messages from stdin, translates to GossipMessage,
// passes to protocol.handle_input(), drains poll_transmit() to stdout.

use std::io::{self, BufRead, Write};
use serde::{Deserialize, Serialize};

// Maelstrom message envelope
#[derive(Deserialize, Serialize)]
struct MaelstromMsg {
    src: String,
    dest: String,
    body: serde_json::Value,
}

fn main() {
    let stdin = io::stdin();
    let stdout = io::stdout();
    let mut out = stdout.lock();

    // Initialize protocol
    // let mut protocol = GossipProtocol::new(...);

    for line in stdin.lock().lines() {
        let line = line.expect("stdin read error");
        let msg: MaelstromMsg = serde_json::from_str(&line)
            .expect("malformed Maelstrom message");

        // Translate Maelstrom message → GossipMessage
        // protocol.handle_input(&gossip_msg, now);

        // Drain outbox → Maelstrom messages
        // while let Some(transmit) = protocol.poll_transmit() {
        //     let response = translate_to_maelstrom(transmit);
        //     serde_json::to_writer(&mut out, &response).unwrap();
        //     out.write_all(b"\n").unwrap();
        //     out.flush().unwrap();
        // }
    }
}

Maelstrom Workloads

Running Maelstrom Tests

# Build the Maelstrom wrapper
cargo build --release --bin maelstrom_gossip

# Run broadcast challenge (gossip convergence)
maelstrom test \
  -w broadcast \
  --bin target/release/maelstrom_gossip \
  --node-count 5 \
  --time-limit 20 \
  --rate 10 \
  --nemesis partition

# Run with stricter timing
maelstrom test \
  -w broadcast \
  --bin target/release/maelstrom_gossip \
  --node-count 25 \
  --time-limit 20 \
  --rate 100 \
  --nemesis partition \
  --latency 100

Maelstrom Output Analysis

After a Maelstrom run, analyze the results:

# Open results in browser
maelstrom serve

# Or parse JSON results directly
cat store/latest/results.edn

Key metrics to check:

• :valid? — Did all operations satisfy the consistency model?
• :lost-count — Messages that were sent but never delivered
• :stable-count — Messages that converged to all nodes
• :latency — Message propagation time distribution

Report format:

MAELSTROM REPORT — {workload}
═════════════════════════════
Nodes:            {count}
Duration:         {seconds}s
Operations:       {count}
Nemesis:          {partition|none|...}

Result:           {PASS|FAIL}

Consistency:
  Valid:          {yes|no}
  Lost messages:  {count} ({percentage}%)
  Stable:         {count} ({percentage}%)

Latency (ms):
  p50:  {value}
  p95:  {value}
  p99:  {value}

Convergence:
  Rounds to full convergence: {count}
  Expected (O(log n)):        {ceil(log2(nodes))}
  Status: {WITHIN BOUND | EXCEEDS BOUND}

{if FAIL}
Anomalies found:
  - {description of consistency violation}
  - {messages lost during partition}
{/if}

Mode B: Full Jepsen

Prerequisites

1. Docker or Vagrant for provisioning test nodes
2. Compiled gossip-rs binaries for the target platform
3. SSH access configured for test nodes
4. Jepsen Clojure framework (or the project's custom test harness)

Cluster Configuration

Based on Yuan et al. (OSDI 2014): 3 nodes suffice for reproducing most distributed failures. Use 5 nodes for partition tolerance testing.

Cluster topology:
  Node 1 (n1): gossip-rs worker + coordination backend
  Node 2 (n2): gossip-rs worker + coordination backend
  Node 3 (n3): gossip-rs worker + coordination backend
  [Node 4 (n4): optional, for partition quorum testing]
  [Node 5 (n5): optional, for partition quorum testing]

Jepsen Workloads

Nemesis Configurations

Running Full Jepsen Tests

# Provision test cluster (Docker)
cd jepsen/gossip-rs
docker compose up -d

# Run shard acquisition linearizability test
lein run test \
  --nodes n1,n2,n3 \
  --workload shard-acquisition \
  --nemesis partition-random-halves \
  --time-limit 60 \
  --concurrency 10

# Run lease exclusivity test (etcd failure pattern)
lein run test \
  --nodes n1,n2,n3 \
  --workload lease-exclusivity \
  --nemesis pause-random-node \
  --time-limit 120 \
  --concurrency 5

# Run combined chaos test
lein run test \
  --nodes n1,n2,n3,n4,n5 \
  --workload full-lifecycle \
  --nemesis combined \
  --time-limit 300 \
  --concurrency 20

Full Jepsen Output Analysis

JEPSEN REPORT — {workload}
══════════════════════════
Nodes:            {count}
Duration:         {seconds}s
Operations:       {count} ({ok}/{fail}/{info})
Nemesis:          {type}
Concurrency:      {threads}

Result:           {PASS|FAIL}

Linearizability:
  Valid history:  {yes|no}
  Checker:        {porcupine|elle|custom}
  Anomalies:      {count}

Invariant checks:
  ┌─────────────────────────────┬────────┬────────┐
  │ Invariant                   │ Status │ Checks │
  ├─────────────────────────────┼────────┼────────┤
  │ Lease exclusivity (S1)      │ PASS   │ 1234   │
  │ Fence monotonicity (S2)     │ PASS   │ 567    │
  │ Terminal irreversibility (S3)│ PASS   │ 89     │
  │ Shard coverage (S4)         │ FAIL   │ 12     │
  └─────────────────────────────┴────────┴────────┘

{if FAIL}
Failing operations:
  t=12.3s  :invoke  acquire-shard  shard-7  worker-2
  t=12.3s  :ok      acquire-shard  shard-7  worker-2  epoch=5
  t=12.5s  NEMESIS: partition [n1,n3] | [n2]
  t=13.1s  :invoke  checkpoint     shard-7  worker-1  epoch=4
  t=13.2s  :ok      checkpoint     shard-7  worker-1  ← VIOLATION: stale epoch accepted

Reproduction:
  lein run test --nodes n1,n2,n3 --workload {workload} --nemesis {nemesis} \
    --time-limit 60 --test-seed {seed}
{/if}

Correctness Properties

These properties must be verified by every Jepsen run. They correspond to the project's invariant catalog and are checked by specific verifiers.

Decision: Maelstrom vs Full Jepsen

Rule of thumb:

• Start with Maelstrom during development
• Graduate to full Jepsen when the system is deployed and integrated
• Run both in CI (Maelstrom per-PR, Jepsen nightly)

Relationship to DST (/sim-run)

                    Speed           Realism          Bugs Found
                    ─────           ───────          ──────────
/sim-run Level 1    ████████████    ██               Logic bugs, state machine errors
/sim-run Level 2    ██████████      ████             Concurrency, timing, lease expiry
/sim-run Level 3    ████████        ██████           Cascading failures, Byzantine
/jepsen Maelstrom   ██████          ████████         Protocol convergence, message loss
/jepsen Full        ██              ██████████████   Integration, deployment, real OS

They test different things at different layers. Both are needed:

• DST finds logic bugs fast (thousands of seeds per second)
• Jepsen finds integration bugs that DST can't (real networking, real OS)

Related Skills

• /sim-run — In-process deterministic simulation (complementary)
• /sim-review — Verify code is DST-compatible
• /sim-scaffold — Generate simulation harnesses and Maelstrom wrappers
• /dist-sys-auditor — Validate distributed systems design decisions