- A
The security group attached to the ALB is blocking inbound traffic from the targets.
Why wrong: Security groups control inbound traffic to the ALB, not from the ALB to targets; this would cause 502 errors if the ALB cannot connect to targets.
- B
The target instances are failing health checks.
When targets fail health checks, the ALB cannot route traffic to them, resulting in 503 errors.
- C
The ALB does not have enough capacity to handle the traffic.
Why wrong: Insufficient capacity would cause the ALB to return 502 errors if it cannot establish connections to targets, but 503 errors are specific to health check failures.
- D
The SSL certificate on the ALB has expired.
Why wrong: An expired SSL certificate would cause TLS handshake failures, resulting in 502 errors, not 503.
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 has an SAP system running on AWS that uses an Application Load Balancer (ALB) to distribute traffic to multiple EC2 instances. The operations team notices that the ALB is returning 503 errors intermittently. 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 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 target instances are failing health checks.
Option B is correct because 503 errors typically indicate that the target instances are unhealthy or not responding. Option A is wrong because SSL certificate expiration causes 502 errors, not 503. Option C is wrong because security group rules blocking traffic would cause timeout or 502 errors. Option D is wrong because insufficient capacity would cause 502 errors if targets are overloaded, but 503 specifically indicates unhealthy targets.
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 attached to the ALB is blocking inbound traffic from the targets.
Why it's wrong here
Security groups control inbound traffic to the ALB, not from the ALB to targets; this would cause 502 errors if the ALB cannot connect to targets.
- ✓
The target instances are failing health checks.
Why this is correct
When targets fail health checks, the ALB cannot route traffic to them, resulting in 503 errors.
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 ALB does not have enough capacity to handle the traffic.
Why it's wrong here
Insufficient capacity would cause the ALB to return 502 errors if it cannot establish connections to targets, but 503 errors are specific to health check failures.
- ✗
The SSL certificate on the ALB has expired.
Why it's wrong here
An expired SSL certificate would cause TLS handshake failures, resulting in 502 errors, not 503.
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
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 PAS-C01 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.
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FAQ
Questions learners often ask
What does this PAS-C01 question test?
Operations and Maintenance — This question tests Operations and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The target instances are failing health checks. — Option B is correct because 503 errors typically indicate that the target instances are unhealthy or not responding. Option A is wrong because SSL certificate expiration causes 502 errors, not 503. Option C is wrong because security group rules blocking traffic would cause timeout or 502 errors. Option D is wrong because insufficient capacity would cause 502 errors if targets are overloaded, but 503 specifically indicates unhealthy targets.
What should I do if I get this PAS-C01 question wrong?
Identify which PAS-C01 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.
About these practice questions
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Last reviewed: Jun 20, 2026
This PAS-C01 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 PAS-C01 exam.
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