The answer is that the security group for the tasks does not allow inbound traffic from the ALB on the health check port. This is the most likely cause because an Application Load Balancer sends health check requests to the target’s IP address on the designated port, and if the task’s security group lacks an inbound rule permitting traffic from the ALB’s security group or CIDR range, those requests are silently dropped, causing the health check to fail and preventing the ECS Fargate task from registering with the target group. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how security groups act as a stateful firewall for containerized workloads, and a common trap is to overlook that the ALB itself is a separate entity requiring explicit ingress rules—unlike network ACLs, security groups default to deny all inbound traffic. Remember the mnemonic: “ALB checks in, tasks let in”—the task’s security group must explicitly allow the health check traffic from the load balancer.
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 launch type. The application is deployed across multiple Availability Zones. Recently, deployments have been failing because new tasks cannot register with the Application Load Balancer (ALB) target group. The health checks are failing. What is the MOST likely cause?
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.
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 for the tasks does not allow inbound traffic from the ALB on the health check port.
Option C is correct because if the security group for the tasks does not allow inbound traffic from the ALB on the health check port, health checks fail. Options A, B, and D do not directly cause health check failures.
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.
✓
The security group for the tasks does not allow inbound traffic from the ALB on the health check port.
Why this is correct
Health checks fail if traffic is blocked.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The ECS service is configured with a desired count of zero.
Why it's wrong here
Would not launch tasks.
✗
The task definition specifies an invalid container image.
Why it's wrong here
Would cause task start failure, not health check failure.
✗
The ECS cluster has insufficient capacity.
Why it's wrong here
Fargate handles capacity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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
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.
Identify which SAP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The security group for the tasks does not allow inbound traffic from the ALB on the health check port. — Option C is correct because if the security group for the tasks does not allow inbound traffic from the ALB on the health check port, health checks fail. Options A, B, and D do not directly cause health check failures.
What should I do if I get this SAP-C02 question wrong?
Identify which SAP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". 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?
Read the scenario before looking for a memorised answer.
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Question Discussion
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