- A
The ALB is not configured with a proper listener rule to forward traffic to the target group.
Why wrong: If there were no listener rule, no traffic would reach the tasks, but the task would still be healthy from the ALB's perspective if the health check succeeds.
- B
The security group attached to the ECS tasks does not allow inbound traffic from the ALB on the health check port.
Without inbound rules allowing traffic from the ALB, health checks will fail.
- C
The deregistration delay (connection draining) is set too high, causing the ALB to think the tasks are unhealthy.
Why wrong: Deregistration delay affects in-flight requests, not health checks.
- D
The health check path is incorrect; it should be '/index.html' instead of '/health'.
Why wrong: The architect confirmed the application correctly responds to '/health'.
Quick Answer
The answer is a misconfigured security group on the ECS tasks. When Amazon ECS with Fargate launches a new task during a scale-out event, each task receives its own elastic network interface (ENI) with an attached security group. If that security group does not explicitly allow inbound traffic from the Application Load Balancer on the container’s health check port, the ALB health check requests are silently dropped, causing the new tasks to fail the health check and be deregistered. This scenario tests your understanding of the network path between the ALB and Fargate tasks, a common trap on the SAP-C02 exam where candidates focus on application code or ALB configuration instead of the security group rules. The key insight is that the container responds correctly internally, so the failure must be at the network layer. Memory tip: think “SG blocks ALB” — if the security group doesn’t let the ALB in, the health check can’t get out.
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. 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 runs a containerized application on Amazon ECS with Fargate. The application uses an Application Load Balancer (ALB) to distribute traffic. The company has configured a target tracking scaling policy based on average memory utilization. During a traffic spike, the ECS service scales out, but the new tasks are immediately deregistered and replaced. The CloudWatch logs show that the new tasks are failing the ALB health check. The health check is configured to ping the '/health' endpoint on the container. The solutions architect verifies that the application container correctly responds to the '/health' endpoint with a 200 status code. What is the MOST likely cause of the health check failures?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue:
"immediately / without restart"Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
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
The security group attached to the ECS tasks does not allow inbound traffic from the ALB on the health check port.
Option C is correct. When using Fargate, each task gets an ENI. If the security group for the tasks does not allow inbound traffic from the ALB on the health check port, the health check will fail. The architect confirmed the application responds correctly, so the issue is likely network connectivity. Option A is wrong because the health check path is correct. Option B is wrong because target group deregistration delay does not cause health check failures. Option D is wrong because the ALB is already configured correctly; the issue is at the task level.
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.
- ✗
The ALB is not configured with a proper listener rule to forward traffic to the target group.
Why it's wrong here
If there were no listener rule, no traffic would reach the tasks, but the task would still be healthy from the ALB's perspective if the health check succeeds.
- ✓
The security group attached to the ECS tasks does not allow inbound traffic from the ALB on the health check port.
Why this is correct
Without inbound rules allowing traffic from the ALB, health checks will fail.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
The deregistration delay (connection draining) is set too high, causing the ALB to think the tasks are unhealthy.
Why it's wrong here
Deregistration delay affects in-flight requests, not health checks.
- ✗
The health check path is incorrect; it should be '/index.html' instead of '/health'.
Why it's wrong here
The architect confirmed the application correctly responds to '/health'.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 SAP-C02 NAT questions on configuration and troubleshooting.
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Continuous Improvement for Existing Solutions — study guide chapter
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FAQ
Questions learners often ask
What does this SAP-C02 question test?
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The security group attached to the ECS tasks does not allow inbound traffic from the ALB on the health check port. — Option C is correct. When using Fargate, each task gets an ENI. If the security group for the tasks does not allow inbound traffic from the ALB on the health check port, the health check will fail. The architect confirmed the application responds correctly, so the issue is likely network connectivity. Option A is wrong because the health check path is correct. Option B is wrong because target group deregistration delay does not cause health check failures. Option D is wrong because the ALB is already configured correctly; the issue is at the task level.
What should I do if I get this SAP-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 SAP-C02 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "immediately / without restart". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
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