The answer is the AllAtOnce deployment configuration causing a partial deployment failure. When CodeDeploy’s AllAtOnce setting is used, it attempts to update every instance in the deployment group simultaneously, with no rolling batches or traffic shifting. If the deployment fails partway—for example, due to a script error or resource constraint on some instances—the process stops, leaving a mixed state where some instances run the new version and others remain on the old version. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how deployment configurations affect failure behavior; a common trap is confusing AllAtOnce with a rolling update or assuming a failed health check would cause a full rollback. Remember that AllAtOnce is all-or-nothing in intent but not in execution—if it breaks mid-stream, you get a split fleet. Memory tip: “AllAtOnce means all at risk—if it fails, you’re left with a mix.”
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.
An organization uses AWS CodePipeline to deploy a web application to Amazon EC2 instances behind an Application Load Balancer. The deployment uses a CodeDeploy action with an in-place deployment configuration. After a recent deployment, some instances are running the old version while others are running the new version. 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 deployment group was configured with the 'AllAtOnce' deployment configuration, and the deployment failed partway through.
Option A is correct because if the deployment group is set to deploy to all instances at once (AllAtOnce), there is no rolling update, and if the deployment fails partway, some instances may be updated and others not. Option B is wrong because a lifecycle hook would not cause partial deployment; it would pause. Option C is wrong because CodeDeploy does not depend on Auto Scaling for in-place deployments. Option D is wrong because a failed health check would cause the deployment to fail entirely, not partially.
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 deployment group is associated with an Auto Scaling group that launched new instances during the deployment.
Why it's wrong here
New instances would be part of the deployment, not cause inconsistency.
✓
The deployment group was configured with the 'AllAtOnce' deployment configuration, and the deployment failed partway through.
Why this is correct
AllAtOnce deploys to all instances simultaneously; a failure may leave some instances updated.
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.
✗
A lifecycle hook is configured to pause the deployment until manual approval.
Why it's wrong here
Manual approval pauses the entire deployment, not partial.
✗
The deployment was configured to use a blue/green strategy, but the target group is misconfigured.
Why it's wrong here
Blue/green would replace all instances, not leave old ones.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 deployment group was configured with the 'AllAtOnce' deployment configuration, and the deployment failed partway through. — Option A is correct because if the deployment group is set to deploy to all instances at once (AllAtOnce), there is no rolling update, and if the deployment fails partway, some instances may be updated and others not. Option B is wrong because a lifecycle hook would not cause partial deployment; it would pause. Option C is wrong because CodeDeploy does not depend on Auto Scaling for in-place deployments. Option D is wrong because a failed health check would cause the deployment to fail entirely, not partially.
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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