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In this lesson, we’ll leverage a pre-configured Amazon CloudWatch dashboard to monitor an Auto Scaling Group (ASG) during a Fault Injection Simulator (FIS) experiment. This setup provides real-time insights into ELB health checks and ASG instance status, enabling you to track scaling behavior and resilience under controlled failures.
  • An AWS FIS experiment configured to terminate or impair EC2 instances
  • An ASG with minCapacity set to a desired level
  • A CloudWatch dashboard pre-populated with the relevant widgets

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Dashboard Widgets Overview

Widget NameMetrics DisplayedPurpose
ELB Host HealthCheckHealthy vs. unhealthy instancesMonitors ELB health check results
ASG Instance ChecksTotal, pending, and in-service instancesTracks scaling events and lifecycle status

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How to Interpret the Charts

  1. ELB Host HealthCheck
    • Baseline: Starts with 2 healthy instances.
    • During FIS: One instance is terminated → healthy count drops to 1.
    • Recovery: ASG’s minCapacity=2 triggers a replacement → healthy count returns to 2.
  2. ASG Instance Checks
    • Pending: Instances being initialized after launch.
    • InService: Fully operational, serving traffic.
    • The graph pattern mirrors the ELB health trend, reflecting when the ASG spins up replacement instances.
The image shows a dashboard with two graphs: one for ELB Host HealthCheck displaying healthy and unhealthy counts, and another for ASG Instance Checks showing total, pending, and in-service instances over time.
If you terminate multiple instances at once or set a high desired capacity, the ASG may launch many replacements simultaneously. Monitor the ASG Instance Checks widget to avoid unexpected resource costs.

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Conclusion

By correlating the ELB Host HealthCheck and ASG Instance Checks charts, you gain a clear, real-time view of how FIS-induced failures impact instance health and auto scaling. This dashboard becomes a powerful tool for validating the resiliency and fault tolerance of your AWS infrastructure.

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References

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