DOP-C02 Incident and Event Response Practice Question
A company runs a critical application on EC2 instances behind an Application Load Balancer (ALB) in an Auto Scaling group. The team wants to automate the response to an instance failure. Which THREE steps should be taken to ensure automatic recovery and notification?
⚠ Common exam trap
It's easy for candidates to confuse CloudWatch alarms (Option A) for instance recovery, but CloudWatch alarms are for monitoring and triggering actions like scaling policies or SNS notifications, not for directly replacing failed instances in an Auto Scaling group.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure Auto Scaling to replace unhealthy instances
Configuring the Auto Scaling group to replace unhealthy instances ensures that when an instance fails health checks, Auto Scaling automatically terminates it and launches a new instance to maintain the desired capacity. This is the core mechanism for automated recovery in an Auto Scaling group, as it directly responds to instance failure without manual intervention.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a CloudWatch alarm to terminate the instance
Why it's wrong here
CloudWatch alarms can trigger instance termination, but this is an anti-pattern when using Auto Scaling. It operates outside the ASG lifecycle and can cause an instance to be terminated even if the ASG is already handling it, leading to race conditions and potential failure to maintain desired capacity. ASG health checks already detect and replace unhealthy instances, so a separate termination alarm introduces unnecessary complexity and risk.
- ✓
Configure Auto Scaling to replace unhealthy instances
Why this is correct
Auto Scaling can be configured with an appropriate health check type (EC2 status checks or ELB/ALB health checks) and a termination policy to automatically detect and replace unhealthy instances. This ensures that the ASG maintains the desired instance count by terminating the unhealthy instance and launching a new one, providing a self-healing architecture for the critical application.
- ✓
Configure the ALB health check to mark instances as unhealthy
Why this is correct
When an Application Load Balancer is configured with a custom health check path, it can report instances as unhealthy if they fail to respond correctly. When the Auto Scaling group uses the ELB health check as its health check type, these ALB health check results are integrated so ASG can replace any instance that is unhealthy at the application layer, going beyond basic EC2 status checks.
- ✓
Set up Amazon SNS notifications for Auto Scaling events
Why this is correct
Configuring SNS notifications for Auto Scaling lifecycle events allows the operations team to receive real-time alerts when instances are launched or terminated. While this does not directly replace unhealthy instances, it is a correct supplementary step because it provides visibility into scaling activities and enables rapid response to any issues, ensuring the team can take action if auto-remediation is insufficient.
- ✗
Create a scaling policy based on CPU utilization
Why it's wrong here
A CPU utilization-based scaling policy adjusts the number of instances in response to load (e.g., adding capacity when CPU is high), but it does not address an instance that is unhealthy or failing health checks. Scaling policies are designed for dynamic capacity management, not for detecting or replacing failed instances; an unhealthy instance may continue to exist and serve traffic poorly until it is explicitly replaced by health check-based mechanisms.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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