DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud 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 uses AWS CodeDeploy for blue/green deployments to an Auto Scaling group. The deployment fails because the new instances do not pass health checks. The DevOps engineer discovers that the health check URL returns a 503 error. 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 target group health check path is '/health' but the application does not serve that endpoint
The health check URL returning a 503 error indicates that the application is not responding to the health check endpoint. Since the target group health check path is configured as '/health' but the application does not serve that endpoint, the ALB considers the instances unhealthy, causing CodeDeploy to fail the deployment. This is the most direct cause because the health check is failing at the application layer, not due to infrastructure issues.
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 target group health check path is '/health' but the application does not serve that endpoint
Why this is correct
A 503 indicates the application is running but not handling the request correctly.
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 CodeDeploy agent on the new instances is not running
Why it's wrong here
A missing agent would cause deployment failure, not a 503 health check.
✗
The security group for the ALB does not allow inbound traffic on port 80
Why it's wrong here
This would cause a timeout, not a 503.
✗
The Auto Scaling group health check type is set to EC2 instead of ELB
Why it's wrong here
This affects Auto Scaling health checks, not the ALB health check path.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse a 503 error with a network-level failure (like a security group blocking traffic) rather than recognizing it as an application-layer response indicating the health check endpoint is missing or misconfigured.
Detailed technical explanation
How to think about this question
Under the hood, the ALB health check sends an HTTP GET request to the configured path (e.g., '/health') and expects a 2xx or 3xx response. A 503 error means the application is running (e.g., behind a reverse proxy like nginx) but the specific route is not defined, causing the web server to return a default error page. In blue/green deployments, CodeDeploy waits for the new instances to pass the ALB health check before routing traffic; if the health check fails, the deployment is rolled back or stopped.
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.
TExam Day Tips
→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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The target group health check path is '/health' but the application does not serve that endpoint — The health check URL returning a 503 error indicates that the application is not responding to the health check endpoint. Since the target group health check path is configured as '/health' but the application does not serve that endpoint, the ALB considers the instances unhealthy, causing CodeDeploy to fail the deployment. This is the most direct cause because the health check is failing at the application layer, not due to infrastructure issues.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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