The answer is that the KMS key policy does not grant kms:Decrypt permission to the CodeBuild service role. This is the most likely cause because even when the CodeBuild role has S3 read access and the key policy lists the role as a principal, the policy must explicitly allow the kms:Decrypt action for CodeBuild to decrypt the encrypted artifact during download. Without this specific permission, the S3 service will deny the request, producing the "Access Denied" error despite the role appearing properly configured. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how KMS key policies interact with service roles—a common trap is assuming that S3 bucket permissions or the CodePipeline service role are at fault, when the issue lies in the key policy’s missing decrypt action. Remember the memory tip: "Decrypt is the key to the key"—if CodeBuild can’t decrypt, it can’t download.
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 CodePipeline to automate builds and deployments. The pipeline has a source stage (Amazon S3) and a build stage (AWS CodeBuild). The build stage is failing with the error: 'Error: Unable to download artifact from S3: Access Denied'. The artifacts are stored in an S3 bucket that is encrypted with AWS KMS. The CodeBuild service role has permissions to read from the S3 bucket and use the KMS key. The team checks that the S3 bucket policy and the KMS key policy allow the CodeBuild role. What is the most likely cause of the failure?
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 KMS key policy does not grant 'kms:Decrypt' permission to the CodeBuild service role.
Option A is correct because CodeBuild needs permissions to decrypt the artifact; if the KMS key policy does not grant 'kms:Decrypt' to the CodeBuild role, access will be denied. Option B is wrong because bucket versioning is not required. Option C is wrong because the artifact bucket is separate from the pipeline bucket. Option D is wrong because CodePipeline service role is not used by CodeBuild to download artifacts.
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 S3 bucket does not have versioning enabled, so CodeBuild cannot retrieve the artifact.
Why it's wrong here
Incorrect: Versioning is not required for artifact download.
✓
The KMS key policy does not grant 'kms:Decrypt' permission to the CodeBuild service role.
Why this is correct
Correct: CodeBuild needs decrypt permission to read encrypted artifacts.
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 CodePipeline service role does not have permission to pass the artifact to CodeBuild.
Why it's wrong here
Incorrect: The pipeline role passes the artifact location, but CodeBuild downloads directly; the error is from CodeBuild.
✗
The artifact is stored in the same S3 bucket used by CodePipeline for its artifacts, causing a conflict.
Why it's wrong here
Incorrect: Different buckets can be used; no conflict.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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 KMS key policy does not grant 'kms:Decrypt' permission to the CodeBuild service role. — Option A is correct because CodeBuild needs permissions to decrypt the artifact; if the KMS key policy does not grant 'kms:Decrypt' to the CodeBuild role, access will be denied. Option B is wrong because bucket versioning is not required. Option C is wrong because the artifact bucket is separate from the pipeline bucket. Option D is wrong because CodePipeline service role is not used by CodeBuild to download artifacts.
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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