- A
Confirm that the load balancer's health check target is pointing to the correct port and path on the instances.
Why wrong: If the health check target is incorrect, instances would be marked unhealthy and eventually terminated by Auto Scaling, not left running.
- B
Check the health check grace period setting in the Auto Scaling group. If it is too long, instances failing health checks may not be terminated quickly.
The health check grace period defines how long after launch before Auto Scaling starts checking health. If set too high, failing instances may persist.
- C
Ensure the instances are sending health check requests to the load balancer.
Why wrong: The ELB sends health checks to the instances; instances do not send health checks to the ELB.
- D
Verify that the security group for the instances allows inbound traffic from the load balancer on the health check port.
Why wrong: Security groups control traffic flow but the health check is initiated by the ELB; if the security group blocks the ELB, the health check would fail and the instance would be marked unhealthy, leading to termination.
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The operations team notices that some instances are failing health checks but are not being terminated by Auto Scaling. What should be investigated to resolve this issue?
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
Check the health check grace period setting in the Auto Scaling group. If it is too long, instances failing health checks may not be terminated quickly.
Option B is correct because the health check grace period in an Auto Scaling group controls how long Auto Scaling waits before checking the health of a newly launched instance. If this grace period is set too long, instances that fail health checks after the grace period expires will not be terminated promptly, leading to the observed behavior where unhealthy instances remain in service. The grace period defaults to 300 seconds, and if it is excessively long, it delays the termination of instances that have already failed health checks.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Confirm that the load balancer's health check target is pointing to the correct port and path on the instances.
Why it's wrong here
If the health check target is incorrect, instances would be marked unhealthy and eventually terminated by Auto Scaling, not left running.
- ✓
Check the health check grace period setting in the Auto Scaling group. If it is too long, instances failing health checks may not be terminated quickly.
Why this is correct
The health check grace period defines how long after launch before Auto Scaling starts checking health. If set too high, failing instances may persist.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Ensure the instances are sending health check requests to the load balancer.
Why it's wrong here
The ELB sends health checks to the instances; instances do not send health checks to the ELB.
- ✗
Verify that the security group for the instances allows inbound traffic from the load balancer on the health check port.
Why it's wrong here
Security groups control traffic flow but the health check is initiated by the ELB; if the security group blocks the ELB, the health check would fail and the instance would be marked unhealthy, leading to termination.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the health check grace period with the load balancer's health check settings, assuming that if health checks are failing, the issue must be with the health check configuration (Option A) rather than the Auto Scaling group's delay in acting on those failures.
Detailed technical explanation
How to think about this question
The health check grace period is defined in the Auto Scaling group's `HealthCheckGracePeriod` parameter, which defaults to 300 seconds. During this period, Auto Scaling does not consider the instance's health status from the load balancer, allowing time for applications to start. If the grace period is set to a very high value (e.g., 3600 seconds), an instance that fails health checks after the grace period expires will not be terminated until the grace period ends, even if it is unhealthy. This is distinct from the load balancer's own health check interval and unhealthy threshold, which determine how quickly the load balancer marks an instance as unhealthy; Auto Scaling then uses that status only after the grace period expires.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check the health check grace period setting in the Auto Scaling group. If it is too long, instances failing health checks may not be terminated quickly. — Option B is correct because the health check grace period in an Auto Scaling group controls how long Auto Scaling waits before checking the health of a newly launched instance. If this grace period is set too long, instances that fail health checks after the grace period expires will not be terminated promptly, leading to the observed behavior where unhealthy instances remain in service. The grace period defaults to 300 seconds, and if it is excessively long, it delays the termination of instances that have already failed health checks.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
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