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AWS Fault Injection Simulator (FIS) helps you test the resilience of your applications by safely inducing faults. In this guide, we’ll define and launch an FIS experiment using three core components: Actions, Targets, and Stop Conditions. You’ll also learn how to apply guardrails to contain the blast radius.

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Table of Contents

  1. Core Components
  2. Prerequisites
  3. Step 1: Define the Action
  4. Step 2: Specify the Target
  5. Step 3: Add a Stop Condition
  6. Step 4: Launch the Experiment
  7. Cleanup
  8. Links and References

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Core Components

ComponentDescriptionExample
ActionThe fault you inject into the system.Terminating an EC2 instance
TargetThe resource(s) on which the action runs.EC2 instances identified by tag Service=api
Stop ConditionA criterion—such as a CloudWatch alarm—that halts and rolls back the experiment when met.CPU utilization > 80% for 5 minutes
Stop conditions are optional but strongly recommended. They prevent runaway experiments and ensure safety.

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Prerequisites

  • AWS CLI v2 installed and configured
  • IAM role with permissions:
    • fis:CreateExperimentTemplate
    • fis:StartExperiment
    • ec2:TerminateInstances
    • cloudwatch:DescribeAlarms
  • EC2 instances tagged with FaultInject=true

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Step 1: Define the Action

We’ll terminate EC2 instances tagged for the experiment. Use the following snippet in your experiment template: 
"actions": {
  "terminateInstances": {
    "actionId": "aws:ec2:terminate-instances",
    "description": "Terminate targeted EC2 instances",
    "parameters": {
      "instances": ["${TargetInstanceIDs}"]
    }
  }
}

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Step 2: Specify the Target

Identify EC2 instances by tag. You can also use resource IDs or ARNs. 
"targets": {
  "TargetInstanceIDs": {
    "resourceType": "aws:ec2:instance",
    "resourceTags": {
      "FaultInject": "true"
    }
  }
}

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Step 3: Add a Stop Condition

Define a CloudWatch alarm that stops the experiment when CPU usage exceeds 80% for 5 minutes: 
"stopConditions": [
  {
    "source": "aws:cloudwatch:alarm",
    "value": "arn:aws:cloudwatch:us-east-1:123456789012:alarm:HighCPUAlarm"
  }
]
Ensure your CloudWatch alarm ARN is correct. A misconfigured stop condition may not trigger, leaving experiments running longer than intended.

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Step 4: Launch the Experiment

Combine the components into a single template and create it with the AWS CLI: 
aws fis create-experiment-template \
  --tags Name=TerminateEC2Test \
  --description "Terminate EC2 instances with guardrails" \
  --role-arn arn:aws:iam::123456789012:role/AWSFISRole \
  --actions file://actions.json \
  --targets file://targets.json \
  --stop-conditions file://stop-conditions.json
Once the template is created, start the experiment: 
aws fis start-experiment \
  --experiment-template-id et-0123456789abcdef0

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Cleanup

After testing, delete your experiment template to avoid orphaned resources: 
aws fis delete-experiment-template \
  --experiment-template-id et-0123456789abcdef0

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