The answer is that the new instances are not passing the configured health check grace period. This is the most likely cause of a CodeDeploy blue/green health check failure causing rollback because the grace period defines how long CodeDeploy waits before starting health checks on newly launched instances; if the application or services on those instances take longer to initialize than the grace period allows, the health checks will fail, triggering an automatic rollback to the stable blue environment. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding of how CodeDeploy integrates with Elastic Load Balancing and Auto Scaling groups during blue/green deployments, and a common trap is confusing a health check failure with a missing CodeDeploy agent—remember that agent issues cause deployment failures, not rollbacks from health checks. A helpful memory tip is “grace before check”: if your app isn’t ready within the grace window, the deployment gets rolled back.
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. 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 with a blue/green deployment strategy for an Amazon EC2 Auto Scaling group. During deployment, the new instances are failing health checks and the deployment is rolling back. 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 new instances are not passing the configured health check grace period.
Option C is correct because failing health checks indicate the new instances are not ready. Option A is incorrect because CodeDeploy agent not running would cause a different error. Option B is incorrect because blue/green typically uses an ELB. Option D is incorrect because the deployment group already targets the ASG.
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 new instances are not passing the configured health check grace period.
Why this is correct
If health checks fail during the grace period, CodeDeploy rolls back.
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 application is not registered with an Elastic Load Balancer.
Why it's wrong here
Blue/green deployments do not require an ELB; they can use an ASG.
✗
The deployment group is not configured to use an Auto Scaling group.
Why it's wrong here
The question states it uses an ASG.
✗
The CodeDeploy agent is not installed on the new instances.
Why it's wrong here
If the agent were missing, the deployment would fail before health checks.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which DOP-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.
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The new instances are not passing the configured health check grace period. — Option C is correct because failing health checks indicate the new instances are not ready. Option A is incorrect because CodeDeploy agent not running would cause a different error. Option B is incorrect because blue/green typically uses an ELB. Option D is incorrect because the deployment group already targets the ASG.
What should I do if I get this DOP-C02 question wrong?
Identify which DOP-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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