This DVA-C02 practice question tests your understanding of security. 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.
Refer to the exhibit. A developer has attached this resource-based policy to an S3 bucket. The Lambda function 'my-function' is still getting access denied when trying to read objects from the bucket. What is the MOST likely reason?
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 condition aws:SourceArn does not match the principal's ARN because the principal is the Lambda execution role, not the function.
Option B is correct because the `aws:SourceArn` condition in the resource-based policy expects the ARN of the principal that is making the request. However, when a Lambda function invokes an S3 operation, the principal is the Lambda execution role (e.g., `arn:aws:iam::123456789012:role/my-function-role`), not the function itself (e.g., `arn:aws:lambda:us-east-1:123456789012:function:my-function`). The condition therefore fails, causing an access denied error even though the function's ARN is listed in the policy.
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 bucket name is incorrect in the policy.
Why it's wrong here
The bucket name example-bucket is used; if it doesn't exist, that could be an issue, but the error is access denied.
✓
The condition aws:SourceArn does not match the principal's ARN because the principal is the Lambda execution role, not the function.
Why this is correct
The source ARN is the function, but the principal is the role; the condition fails.
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 Lambda function's execution role does not have s3:GetObject permission.
Why it's wrong here
The bucket policy grants the permission, but the condition might not be met.
✗
The policy denies s3:GetObject for the Lambda function.
Why it's wrong here
The policy grants Allow.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the ARN of the Lambda function with the ARN of the Lambda execution role, assuming the `aws:SourceArn` condition should match the function ARN, when in fact it must match the principal (the role) that performs the S3 operation.
Detailed technical explanation
How to think about this question
Under the hood, S3 evaluates both identity-based policies (attached to the IAM principal, e.g., the Lambda execution role) and resource-based policies (attached to the bucket). The `aws:SourceArn` condition key is used to prevent cross-service confused deputy problems, but it must match the ARN of the principal (the IAM role) that actually makes the API call, not the ARN of the service resource (the Lambda function). In practice, if you need to restrict access to a specific Lambda function, you should use `aws:SourceAccount` or the function's ARN in the `Principal` element, not in the `Condition` block.
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 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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The condition aws:SourceArn does not match the principal's ARN because the principal is the Lambda execution role, not the function. — Option B is correct because the `aws:SourceArn` condition in the resource-based policy expects the ARN of the principal that is making the request. However, when a Lambda function invokes an S3 operation, the principal is the Lambda execution role (e.g., `arn:aws:iam::123456789012:role/my-function-role`), not the function itself (e.g., `arn:aws:lambda:us-east-1:123456789012:function:my-function`). The condition therefore fails, causing an access denied error even though the function's ARN is listed in the policy.
What should I do if I get this DVA-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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