The answer is that the IAM role lacks a trust policy allowing CodeBuild to assume it. Even though the CodeBuildServiceRole has a policy granting codecommit:GitPull on all repositories, the role itself must include a trust relationship that explicitly permits the CodeBuild service to assume that role via sts:AssumeRole. Without this trust policy, CodeBuild cannot adopt the role’s identity, so any attached permissions are never evaluated, resulting in the access denied error when fetching source code from CodeCommit. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding that IAM role trust policies are a prerequisite for service-to-role delegation, not just resource-based permissions. A common trap is focusing solely on the action policy while overlooking the trust policy, which must specify the CodeBuild service principal. Remember: trust first, then permissions—if CodeBuild can’t assume the role, the policy is invisible.
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.
Network Topology
A DevOps engineer runs the above AWS CLI commands and notices that the CodeBuild project 'my-project' exists but builds fail with the error 'Access Denied' when trying to fetch source code from CodeCommit. The IAM role 'CodeBuildServiceRole' has a policy that allows 'codecommit:GitPull' on all repositories. 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 IAM role does not have a trust policy that allows CodeBuild to assume the role.
The error 'Access Denied' when CodeBuild tries to fetch source code from CodeCommit typically indicates that the IAM role CodeBuild is using does not have the necessary permissions to perform the action. Even though the role 'CodeBuildServiceRole' has a policy allowing 'codecommit:GitPull', the role itself must have a trust policy that allows the CodeBuild service to assume it. Without a proper trust policy, CodeBuild cannot assume the role, and any attached permissions are irrelevant, leading to an access denied error.
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 IAM role does not have permissions to access the CodeCommit repository.
Why it's wrong here
The policy allows GitPull.
✓
The IAM role does not have a trust policy that allows CodeBuild to assume the role.
Why this is correct
CodeBuild must be able to assume the role via trust policy.
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 CodeCommit repository does not exist.
Why it's wrong here
The CLI output shows the repository location, implying it exists.
✗
The source location in the build project is incorrect.
Why it's wrong here
The location is correct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often focus on the IAM policy permissions (e.g., 'codecommit:GitPull') and overlook the necessity of a trust policy, assuming that if the policy allows the action, the role is automatically usable by the service.
Trap categories for this question
Command / output trap
The CLI output shows the repository location, implying it exists.
Detailed technical explanation
How to think about this question
Under the hood, AWS CodeBuild uses the IAM role specified in the project's 'serviceRole' field to make API calls to other services like CodeCommit. The role must have a trust policy with a 'Principal' set to 'codebuild.amazonaws.com' and an 'Action' of 'sts:AssumeRole'. Without this trust relationship, the STS AssumeRole call fails, and CodeBuild cannot obtain temporary credentials, resulting in an 'Access Denied' error even if the role's permissions are correct. This is a common misconfiguration when setting up cross-service integrations.
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 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 IAM role does not have a trust policy that allows CodeBuild to assume the role. — The error 'Access Denied' when CodeBuild tries to fetch source code from CodeCommit typically indicates that the IAM role CodeBuild is using does not have the necessary permissions to perform the action. Even though the role 'CodeBuildServiceRole' has a policy allowing 'codecommit:GitPull', the role itself must have a trust policy that allows the CodeBuild service to assume it. Without a proper trust policy, CodeBuild cannot assume the role, and any attached permissions are irrelevant, leading to an access denied error.
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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