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The scenario command runs predefined chaos testing scenarios that simulate real-world failure patterns like network partitions, outages, and performance degradation.
Syntax cruel scenario < nam e > [options]
Arguments The name of the scenario to run Available scenarios:
networkPartition - Simulates network partition with intermittent connectivityhighLatency - Simulates high network latency conditionsdegraded - Simulates degraded service performanceoutage - Simulates complete service outagerecovery - Simulates service recovery from failures Options Duration of the scenario in milliseconds
Available Scenarios Network Partition Simulates network partition where connectivity is intermittent:
cruel scenario networkPartition --duration 10000
This scenario mimics network splits common in distributed systems, where some nodes can communicate while others cannot.
High Latency Simulates high network latency conditions:
cruel scenario highLatency --duration 8000
Use this to test how your application behaves under slow network conditions.
Simulates degraded service performance:
cruel scenario degraded --duration 12000
Tests partial failures where the service is slow but still functional.
Service Outage Simulates complete service outage:
cruel scenario outage --duration 5000
Tests how your application handles total service unavailability.
Recovery Simulates service recovery from failures:
cruel scenario recovery --duration 15000
Tests how your application handles gradual service recovery.
Basic Usage Network partition
High latency with custom duration
Service outage
Long-running degraded scenario
cruel scenario networkPartition
Output Example $ cruel scenario outage --duration 5000 running scenario: outage duration: 5.00s scenario complete calls: 47 failures: 42 timeouts: 5
How Scenarios Work Scenarios are predefined chaos configurations that run for a specified duration:
// From cli.ts:270-275 cruel . scenario ( name , { chaos: cruel . presets [ name ] || { fail: 0.5 }, duration , }) await cruel . play ( name )
Each scenario:
Configures chaos parameters from presets or defaults
Runs for the specified duration
Collects statistics about failures injected
Reports results when complete
Scenario Statistics After a scenario completes, you’ll see:
calls : Total number of function calls made during the scenariofailures : Number of failures injectedtimeouts : Number of timeouts injected
These statistics help you understand the chaos impact.
Duration Configuration The duration parameter controls how long the scenario runs:
# 5 seconds (default) cruel scenario outage --duration 5000 # 30 seconds cruel scenario degraded --duration 30000 # 2 minutes cruel scenario networkPartition --duration 120000
Duration is specified in milliseconds.
Use Cases Integration Testing Run scenarios during integration tests to validate resilience:
# Start scenario in background cruel scenario degraded --duration 60000 & # Run your integration tests npm run test:integration # Scenario automatically stops after 60s
Chaos Engineering Exercises Run scenarios during game days or chaos engineering exercises:
# Simulate a 10-minute network partition cruel scenario networkPartition --duration 600000
Production Validation Validate production resilience with controlled chaos:
# Run a 5-minute degraded performance scenario cruel scenario degraded --duration 300000
Load Testing with Chaos Combine scenarios with load testing:
# Start chaos scenario cruel scenario highLatency --duration 30000 & # Run load test while chaos is active cruel benchmark https://api.example.com --count 500 --concurrent 25
Scenario Combinations Run multiple scenarios in sequence:
Sequential scenarios
Automated chaos
cruel scenario networkPartition --duration 10000 cruel scenario highLatency --duration 10000 cruel scenario outage --duration 5000 cruel scenario recovery --duration 15000
Error Handling If you forget to provide a scenario name:
$ cruel scenario error: scenario name required available: networkPartition, highLatency, degraded, outage, recovery
The CLI lists all available scenarios to help you choose.
Scenario Presets Scenarios use chaos presets under the hood. If a preset exists with the same name as the scenario, it’s used:
// From cli.ts:271 chaos : cruel . presets [ name ] || { fail: 0.5 }
Otherwise, a default configuration with 50% failure rate is applied.
Monitoring Scenarios View accumulated statistics during or after scenarios:
# Run scenario in background cruel scenario degraded --duration 60000 & # Check statistics while running cruel stats # Check again after completion cruel stats
Best Practices Start with Short Durations Begin with short durations to understand impact:
cruel scenario outage --duration 3000
Monitor Your System Watch system metrics while scenarios run:
Application logs
Error rates
Response times
Resource utilization
Document Results Record scenario results for analysis:
cruel scenario networkPartition --duration 10000 > results.txt
Run During Low Traffic For production testing, run during low-traffic periods:
# Run during maintenance window cruel scenario degraded --duration 300000
Combine with Observability Use with monitoring tools to see the full impact:
# Start scenario cruel scenario highLatency --duration 60000 & # Watch metrics in your monitoring dashboard # Grafana, Datadog, New Relic, etc.
Real-World Scenario Examples Simulating AWS Region Failure cruel scenario outage --duration 300000 # 5 minutes
Simulating Network Congestion cruel scenario highLatency --duration 600000 # 10 minutes
Simulating Database Slowdown cruel scenario degraded --duration 180000 # 3 minutes
Simulating Split Brain cruel scenario networkPartition --duration 120000 # 2 minutes