- 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.
Quick Answer
The answer is to check the health check grace period setting in the Auto Scaling group, as an excessively long grace period prevents Auto Scaling from terminating instances that fail health checks shortly after launch. This grace period is a timer that begins when an instance enters service, during which Auto Scaling waits before checking the instance’s health status; if set too high, a failing instance remains protected from termination, allowing it to accumulate errors. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this concept tests your understanding of how Auto Scaling integrates with Elastic Load Balancing health checks, often appearing as a trap where candidates confuse network-level issues (like security groups) with timing-based configuration. A common memory tip is to think of the grace period as a “free pass” timer—if it’s too long, unhealthy instances get a free pass to stay alive, so always verify this setting when instances fail checks but aren’t replaced.
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 C is correct because if the health check grace period is too long, instances that fail shortly after launch may not be terminated promptly. Option A is wrong because security groups allow traffic but do not affect health check initiation. Option B is wrong because ELB health checks are sent to the instances, not the other way. Option D is wrong because the load balancer is the one performing health checks.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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
Static NAT maps one inside address to one outside address.
- ✗
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: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
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Monitoring and Logging — study guide chapter
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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 — Static NAT maps one inside address to one outside address..
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 C is correct because if the health check grace period is too long, instances that fail shortly after launch may not be terminated promptly. Option A is wrong because security groups allow traffic but do not affect health check initiation. Option B is wrong because ELB health checks are sent to the instances, not the other way. Option D is wrong because the load balancer is the one performing health checks.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
This DOP-C02 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 DOP-C02 exam.
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