---

name: chaos-engineering description: "Chaos engineering for distributed systems: design and run chaos experiments to proactively discover weaknesses before they cause outages. Use when user mentions chaos, fault injection, resilience testing, GameDays, chaos monkey,LitmusChaos, Gremlin, steady-state hypothesis, or when building信頼性 into microservices."

Chaos Engineering — Proactive Resilience Discovery

Core Philosophy

"Break things on purpose to build unbreakable systems."

Chaos engineering is the discipline of experimenting on a system to build confidence in its resilience. Unlike reactive debugging, it proactively injects faults before users notice them.

Key Principle: Steady-State Hypothesis First

Every experiment starts with a steady-state hypothesis — a measurable statement about your system's behavior under normal conditions.

Steady State = "Normal behavior we expect to observe"
Hypothesis   = "Injecting fault X will [not change / degrade] the steady state"

Never run chaos without first defining steady state.

Experiment Design Pattern

1. Define steady-state hypothesis
2. Inject the smallest possible fault
3. Monitor for deviation from steady state
4. Roll back immediately if hypothesis fails
5. Automate and repeat

Common Faults to Inject

Network Layer

Fault	Command/Method	Impact
Latency	tc qdisc add dev eth0 netem delay 100ms	API timeouts
Packet loss	tc qdisc add dev eth0 netem loss 5%	Intermittent errors
DNS failure	/etc/hosts manipulation	Service discovery breaks
Partition	iptables -A INPUT -s <ip>	Network split

Resource Layer

Fault	Method	Impact
CPU spike	stress-ng --cpu 1 --timeout 30s	Throttling, slow responses
Memory leak	Allocate until OOM	Pod evictions
Disk full	dd if=/dev/zero of=/tmp/bigfile	Write failures
File descriptor exhaustion	ulimit -n 1024 in container	Connection pooling breaks

Application Layer

Fault	Method	Impact
Kill pod	kubectl delete pod	Restart tolerance
Container restart	docker restart	Session/state recovery
Config map change	kubectl patch	Behavior drift
Secret deletion	kubectl delete secret	Auth failures

External Dependency Layer

Fault	Method	Impact
Downstream timeout	TC delay on egress	Cascade failure
5xx simulation	iptables redirect	Error budget burn
Dependency pod kill	kubectl delete	Circuit breaker validation

Tooling Landscape

Kubernetes-Native

• LitmusChaos (CNCF, open source) — Custom Resource Definition for chaos, declarative YAML experiments
• Chaos Mesh (PingCAP, CNCF) — Kubernetes-native, Web UI, broad fault library
• Kube-burner — Load/stress focused, for high-scale experiments

Host/VM Layer

• Gremlin (commercial) — Agent-based, attack categories, safety features
• ChaoS Monkey (Netflix) — Terminates random instances in AWS
• Pumba — Docker/Kubernetes chaos, container-level faults
• toxiproxy — Network partition/slowdown simulation for local dev

Code/Unit Layer

• Fault injection in tests — Simulate errors in unit tests (see patterns below)
• Toxiproxy-go / toxiproxy — Programmatic network fault injection

Experiment YAML Patterns (LitmusChaos)

Pod Kill Experiment

apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: pod-kill-chaos
spec:
  engineState: active
  appinfo:
    appns: production
    applabel: "app=api-gateway"
  chaosServiceAccount: litmus-admin
  experiments:
  - name: pod-delete
    spec:
      components:
        env:
        - name: TOTAL_CHAOS_DURATION
          value: '30'
        - name: CHAOS_INTERVAL
          value: '10'
        - name: FORCE
          value: 'false'

Network Latency Experiment

spec:
  components:
    env:
    - name: NETWORK_LATENCY
      value: '6000'        # 6000ms = 6s latency
    - name: TARGET_PODS
      value: 'http-api'    # pods matching label
    - name: DESTINATION_PORTS
      value: '8080'

Test Integration Patterns

Python: Simulate External API Failure

import pytest
from unittest.mock import patch

@pytest.mark.parametrize("fault", ["timeout", "500", "connection_refused"])
def test_order_service_resilience(fault):
    """Order service should degrade gracefully under API faults."""
    with patch("orders.clients.payment") as mock_payment:
        if fault == "timeout":
            mock_payment.charge.side_effect = TimeoutError()
        elif fault == "500":
            mock_payment.charge.side_effect = HTTPError(500)
        else:
            mock_payment.charge.side_effect = ConnectionRefusedError()

        # System under test
        result = order_service.process_order(TEST_ORDER)

        # Assertions: graceful degradation, no crash
        assert result.status in ("pending_retry", "failed_isolated")
        assert not result.charged  # don't charge if payment uncertain

Go: Chaos in Unit Tests

func TestInventoryService_TimeoutResilience(t *testing.T) {
    // Simulate slow DB with context deadline
    ctx, cancel := context.WithTimeout(context.Background(), 1*time.Millisecond)
    defer cancel()

    svc := NewInventoryService(mockDB{latency: 5 * time.Second})

    // Should return context deadline exceeded, not panic
    _, err := svc.GetStock(ctx, "SKU-123")

    if err == nil {
        t.Fatal("expected context deadline error under slow DB")
    }
    if !strings.Contains(err.Error(), "deadline") {
        t.Errorf("wrong error type: %v", err)
    }
}

Bash: Network Fault Injection

#!/bin/bash
# Inject 500ms latency on eth0 for 60 seconds, then auto-rollback
INTERFACE="${INTERFACE:-eth0}"
DELAY_MS="${DELAY_MS:-500}"

cleanup() {
    echo "[chaos] Removing netem rule..."
    tc qdisc del dev "$INTERFACE" root 2>/dev/null || true
}
trap cleanup EXIT

echo "[chaos] Injecting ${DELAY_MS}ms latency on $INTERFACE..."
tc qdisc add dev "$INTERFACE" root netem delay "${DELAY_MS}ms" limit 1000000

echo "[chaos] Running for 60s... (Ctrl+C to abort)"
sleep 60

echo "[chaos] Experiment complete."

GameDay Playbook

A GameDay is a team-wide chaos experiment event.

Pre-GameDay (1 week before):
  - Define hypotheses and acceptance criteria
  - Identify blast radius — must be contained
  - Prepare rollback procedures
  - Notify on-call and stakeholders
  - Set up monitoring dashboards

GameDay:
  Step 1: Baseline measurement (10 min)
    → Capture normal metrics: latency p50/p95/p99, error rate, throughput

  Step 2: Small fault injection (20 min)
    → Start with latency injection (lowest blast radius)
    → Observe monitoring dashboards in real time
    → Document observations vs. hypothesis

  Step 3: Escalate fault scope (30 min)
    → Kill a single pod → kill 25% → kill 50%
    → Document failure cascade patterns

  Step 4: Roll back and reflect (10 min)

Post-GameDay:
  - Write formal experiment report
  - Prioritize discovered gaps by blast radius × frequency
  - Create follow-up tickets for each gap
  - Update runbooks with new failure modes

Experiment Report Template

## Chaos Experiment Report: [Name]

### Hypothesis
[What we expected to happen]

### Steady State Baseline
- Metric A: [value] (pre-experiment)
- Metric B: [value] (pre-experiment)

### Fault Injected
- Type: [network/resource/app/external]
- Details: [specific configuration]

### Results
| Metric | Baseline | During Experiment | Deviation |
|--------|----------|-------------------|-----------|
| p99 latency | 120ms | 3400ms | +2833% |
| Error rate | 0.1% | 8.3% | +820% |

### Conclusion
✅ Hypothesis confirmed / ❌ Hypothesis disproved

### Findings
1. [Finding 1]
2. [Finding 2]

### Action Items
| Action | Severity | Owner |
|--------|----------|-------|
| Add circuit breaker | P1 | @team-backend |
| Increase replica count | P2 | @team-infra |

Safety Rules (NEVER Violate)

• Never experiment in production without blast-radius containment
• Always have a rollback button —tc qdisc del, kubectl rollout undo
• Never run multiple experiments simultaneously on the same system
• Always define steady state before injecting faults
• Never increase blast radius during an active experiment
• Always stop the experiment immediately if customer-facing metrics degrade

Tool Selection Guide

Environment	Recommended Tool
Kubernetes (open source)	LitmusChaos or Chaos Mesh
AWS (managed)	AWS Fault Injection Simulator (FIS)
Docker containers	Pumba
Local dev / testing	Toxiproxy
Go services	Programmatic injection in unit tests
Python services	unittest.mock + pytest parametrization
Full stack (mixed)	Gremlin (commercial)

When to Trigger This Skill

This skill activates when the user mentions:

• Running chaos experiments
• Fault injection testing
• GameDays or resilience testing
• LitmusChaos, Chaos Mesh, Gremlin, Pumba
• Breaking things on purpose
• Microservices reliability
• Circuit breakers, bulkheads, timeouts
• Netflix Chaos Monkey

---

Last updated: 2026-03-28