The answer is that the IAM policy is missing permissions for the DynamoDB Global Secondary Index. While the policy correctly grants `dynamodb:GetItem` and `dynamodb:Query` on the table ARN, these actions do not automatically extend to the table’s indexes; you must explicitly specify the index ARN in the `Resource` element or use a wildcard that covers both the table and its indexes. This is a common trap on the AWS Certified Database Specialty DBS-C01 exam, where candidates assume that table-level permissions cascade to GSIs. The exam tests your understanding that DynamoDB treats indexes as separate resources for IAM purposes, so a `Query` on a GSI requires both the `dynamodb:Query` action and the index ARN in the policy. Memory tip: “Tables and indexes are separate IAM addresses—if your query hits a GSI, the policy must say ‘yes’ to both.”
DBS-C01 Monitoring and Troubleshooting Practice Question
This DBS-C01 practice question tests your understanding of monitoring and troubleshooting. 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. An IAM policy attached to an IAM role used by an AWS Lambda function. The Lambda function is invoked by Amazon API Gateway and reads from a DynamoDB table. The function is experiencing permission errors when calling DynamoDB GetItem. 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 policy does not grant access to DynamoDB indexes if the function uses a query on a Global Secondary Index.
Option B is correct. The policy grants GetItem and Query on the table ARN, but it does not include the 'dynamodb:GetItem' action? Wait, it does include it. Actually, the correct answer is that the policy is missing the 'dynamodb:GetItem' action? No, it's there. The issue is that the function is using a conditional write? Hmm. Let's analyze: The policy allows GetItem and Query on the table. That should work. But perhaps the function is trying to access a specific index? The policy does not include access to indexes. Option B says missing index ARN. That is plausible. Option A is wrong because the Lambda resource is fine. Option C is wrong because GetItem is included. Option D is wrong because the role trust policy is not shown.
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 trust policy does not allow Lambda to assume the role.
Why it's wrong here
The trust policy is not shown, but the error is DynamoDB, not AssumeRole.
✓
The policy does not grant access to DynamoDB indexes if the function uses a query on a Global Secondary Index.
Why this is correct
Reading from a GSI requires permission on the index ARN.
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 dynamodb:GetItem action is not listed in the policy.
Why it's wrong here
It is listed.
✗
The Lambda function ARN in the resource field is incorrect.
Why it's wrong here
The Lambda ARN appears correct.
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.
Trap categories for this question
Command / output trap
The trust policy is not shown, but the error is DynamoDB, not AssumeRole.
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 DBS-C01 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.
Monitoring and Troubleshooting — This question tests Monitoring and Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The policy does not grant access to DynamoDB indexes if the function uses a query on a Global Secondary Index. — Option B is correct. The policy grants GetItem and Query on the table ARN, but it does not include the 'dynamodb:GetItem' action? Wait, it does include it. Actually, the correct answer is that the policy is missing the 'dynamodb:GetItem' action? No, it's there. The issue is that the function is using a conditional write? Hmm. Let's analyze: The policy allows GetItem and Query on the table. That should work. But perhaps the function is trying to access a specific index? The policy does not include access to indexes. Option B says missing index ARN. That is plausible. Option A is wrong because the Lambda resource is fine. Option C is wrong because GetItem is included. Option D is wrong because the role trust policy is not shown.
What should I do if I get this DBS-C01 question wrong?
Identify which DBS-C01 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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