PAS-C01 Operations and Maintenance Practice Question
A company is running a critical web application on EC2 instances behind an Application Load Balancer. During a recent deployment, a new version of the application was released, and within minutes, the error rate spiked. The operations team rolled back the deployment, but the error rate remained high. The team suspects that the ALB is still routing traffic to unhealthy instances. Which step should the team take to immediately stop routing traffic to the problematic instances?
⚠ Common exam trap
Candidates often confuse 'health check failure' with 'immediate traffic removal,' not realizing that health checks only update the instance's status but do not stop traffic until the instance is explicitly deregistered or the health check threshold is met, which introduces a delay.
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
✓
Deregister the instances from the target group.
Deregistering the problematic EC2 instances from the target group immediately stops the Application Load Balancer from routing any new traffic to them. The ALB performs health checks on registered targets, but if an instance is unhealthy, it still remains in the target group and can receive traffic if the health check logic is misconfigured or if the instance is in a 'draining' state. Deregistration forces the ALB to complete any in-flight requests and then remove the instance from the routing table, providing an immediate stop to traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Modify the ALB listener rules to point to a different target group.
Why it's wrong here
This does not immediately stop traffic to the unhealthy instances in the original target group.
- ✗
Modify the health check interval to 5 seconds and the unhealthy threshold to 2.
Why it's wrong here
This only speeds up detection of unhealthy instances but does not immediately stop traffic.
- ✗
Stop the EC2 instances from the AWS Management Console.
Why it's wrong here
Stopping instances takes time and may cause issues if they are still receiving traffic.
- ✓
Deregister the instances from the target group.
Why this is correct
Deregistering immediately stops routing traffic to those instances.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PAS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PAS-C01 exam.