Chaos Engineer

# Chaos Engineer

## When to Use This Skill

- Designing and executing chaos experiments
- Implementing failure injection frameworks (Chaos Monkey, Litmus, etc.)
- Planning and conducting game day exercises
- Building blast radius controls and safety mechanisms
- Setting up continuous chaos testing in CI/CD
- Improving system resilience based on experiment findings

## Core Workflow

1. **System Analysis** - Map architecture, dependencies, critical paths, and failure modes
2. **Experiment Design** - Define hypothesis, steady state, blast radius, and safety controls
3. **Execute Chaos** - Run controlled experiments with monitoring and quick rollback
4. **Learn & Improve** - Document findings, implement fixes, enhance monitoring
5. **Automate** - Integrate chaos testing into CI/CD for continuous resilience

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Experiments | `references/experiment-design.md` | Designing hypothesis, blast radius, rollback |
| Infrastructure | `references/infrastructure-chaos.md` | Server, network, zone, region failures |
| Kubernetes | `references/kubernetes-chaos.md` | Pod, node, Litmus, chaos mesh experiments |
| Tools & Automation | `references/chaos-tools.md` | Chaos Monkey, Gremlin, Pumba, CI/CD integration |
| Game Days | `references/game-days.md` | Planning, executing, learning from game days |

## Safety Checklist

Non-obvious constraints that must be enforced on every experiment:

- **Steady state first** — define and verify baseline metrics before injecting any failure
- **Blast radius cap** — start with the smallest possible impact scope; expand only after validation
- **Automated rollback ≤ 30 seconds** — abort path must be scripted and tested before the experiment begins
- **Single variable** — change only one failure condition at a time until behaviour is well understood
- **No production without safety nets** — customer-facing environments require circuit breakers, feature flags, or canary isolation
- **Close the loop** — every experiment must produce a written learning summary and at least one tracked improvement

## Output Templates

When implementing chaos engineering, provide:
1. Experiment design document (hypothesis, metrics, blast radius)
2. Implementation code (failure injection scripts/manifests)
3. Monitoring setup and alert configuration
4. Rollback procedures and safety controls
5. Learning summary and improvement recommendations

## Concrete Example: Pod Failure Experiment (Litmus Chaos)

The following shows a complete experiment — from hypothesis to rollback — using Litmus Chaos on Kubernetes.

### Step 1 — Define steady state and apply the experiment

```bash
# Verify baseline: p99 latency < 200ms, error rate < 0.1%
kubectl get deploy my-service -n production
kubectl top pods -n production -l app=my-service
```

### Step 2 — Create and apply a Litmus ChaosEngine manifest

```yaml
# chaos-pod-delete.yaml
apiVersion: litmuschaos.io/v1alpha1
kind: ChaosEngine
metadata:
  name: my-service-pod-delete
  namespace: production
spec:
  appinfo:
    appns: production
    applabel: "app=my-service"
    appkind: deployment
  # Limit blast radius: only 1 replica at a time
  engineState: active
  chaosServiceAccount: litmus-admin
  experiments:
    - name: pod-delete
      spec:
        components:
          env:
            - name: TOTAL_CHAOS_DURATION
              value: "60"          # seconds
            - name: CHAOS_INTERVAL
              value: "20"          # delete one pod every 20s
            - name: FORCE
              value: "false"
            - name: PODS_AFFECTED_PERC
              value: "33"          # max 33% of replicas affected
```

```bash
# Apply the experiment
kubectl apply -f chaos-pod-delete.yaml

# Watch experiment status
kubectl describe chaosengine my-service-pod-delete -n production
kubectl get chaosresult my-service-pod-delete-pod-delete -n production -w
```

### Step 3 — Monitor during the experiment

```bash
# Tail application logs for errors
kubectl logs -l app=my-service -n production --since=2m -f

# Check ChaosResult verdict when complete
kubectl get chaosresult my-service-pod-delete-pod-delete \
  -n production -o jsonpath='{.status.experimentStatus.verdict}'
```

### Step 4 — Rollback / abort if steady state is violated

```bash
# Immediately stop the experiment
kubectl patch chaosengine my-service-pod-delete \
  -n production --type merge -p '{"spec":{"engineState":"stop"}}'

# Confirm all pods are healthy
kubectl rollout status deployment/my-service -n production
```

## Concrete Example: Network Latency with toxiproxy

```bash
# Install toxiproxy CLI
brew install toxiproxy   # macOS; use the binary release on Linux

# Start toxiproxy server (runs alongside your service)
toxiproxy-server &

# Create a proxy for your downstream dependency
toxiproxy-cli create -l 0.0.0.0:22222 -u downstream-db:5432 db-proxy

# Inject 300ms latency with 10% jitter — blast radius: this proxy only
toxiproxy-cli toxic add db-proxy -t latency -a latency=300 -a jitter=30

# Run your load test / observe metrics here ...

# Remove the toxic to restore normal behaviour
toxiproxy-cli toxic remove db-proxy -n latency_downstream
```

## Concrete Example: Chaos Monkey (Spinnaker / standalone)

```bash
# chaos-monkey-config.yml — restrict to a single ASG
deployment:
  enabled: true
  regionIndependence: false
chaos:
  enabled: true
  meanTimeBetweenKillsInWorkDays: 2
  minTimeBetweenKillsInWorkDays: 1
  grouping: APP           # kill one instance per app, not per cluster
  exceptions:
    - account: production
      region: us-east-1
      detail: "*-canary"  # never kill canary instances

# Apply and trigger a manual kill for testing
chaos-monkey --app my-service --account staging --dry-run false
```

[Documentation](https://jeffallan.github.io/claude-skills/skills/devops/chaos-engineer/)