The answer is that the security group is blocking the health check traffic. Even when an EC2 instance is in the 'running' state, its security group acts as a virtual firewall that must explicitly allow inbound traffic from the Application Load Balancer’s subnets on the health check port and protocol. If the security group denies this traffic, the ALB health check fails because the target never receives the request, regardless of the instance’s operational status. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your ability to distinguish between instance-level issues (like CPU credits or impaired status) and network-layer misconfigurations, which are a common trap for candidates who assume a running instance automatically passes health checks. A useful memory tip is to think of the security group as the bouncer at the door: even if the party inside is running fine, no one gets in without the right invitation.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new 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.
Network Topology
Refer to the exhibit. An architect is troubleshooting an EC2 instance that is not responding to health checks from an Application Load Balancer. The instance is in the 'running' state. Which of the following 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 is blocking the health check traffic.
Option D is correct because a running instance may still have a failed application or security group blocking health checks. Option A is wrong because the instance is running, so it's not stopped. Option B is wrong because CPU credits affect performance but not health check responses. Option C is wrong because the instance status is running, not impaired.
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 is blocking the health check traffic.
Why this is correct
A misconfigured security group can block health checks even if the instance is running.
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 instance is in a stopped state.
Why it's wrong here
The output shows the instance is running, not stopped.
✗
The instance is impaired due to an AWS issue.
Why it's wrong here
Instance status checks would show impairment, but the output shows running state.
✗
The instance has exhausted its CPU credits.
Why it's wrong here
CPU credits affect performance but do not cause health check failures; the instance would still respond.
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.
Trap categories for this question
Command / output trap
The output shows the instance is running, not stopped.
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
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.
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.
Design for New Solutions — This question tests Design for New 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 is blocking the health check traffic. — Option D is correct because a running instance may still have a failed application or security group blocking health checks. Option A is wrong because the instance is running, so it's not stopped. Option B is wrong because CPU credits affect performance but not health check responses. Option C is wrong because the instance status is running, not impaired.
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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