The answer is that the resource ARN in the policy uses an incorrect RDS resource ID. This is the most likely reason for the connection failure because IAM database authentication for RDS MySQL requires the resource ARN to contain the exact RDS resource identifier—the unique 'db-xxxxx' string from the RDS console—rather than the DB instance name or endpoint. When the ARN does not match the target instance’s resource ID, the IAM policy fails to authorize the connection, even if the database user name and action are correct. On the AWS Certified Database Specialty DBS-C01 exam, this concept tests your understanding of the precise ARN format for RDS resources, a common trap where candidates confuse the instance name with the resource ID. A helpful memory tip is to think of the resource ID as the database’s internal serial number, not its friendly name—always copy the 'db-xxxxx' value directly from the console to avoid mismatches.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. 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.
Exhibit
Consider the following IAM policy attached to an RDS DB instance:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": "rds-db:connect",
"Resource": "arn:aws:rds-db:us-east-1:123456789012:dbuser:db-ABCDEFGHIJKL01234/db_user1"
}
]
}
Refer to the exhibit. A database specialist is troubleshooting an issue where an application cannot connect to an RDS for MySQL instance using IAM database authentication. The application uses the database user 'db_user1'. The IAM policy shown is attached to the IAM role used by the application. What is the most likely reason for the connection 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.
Consider the following IAM policy attached to an RDS DB instance:
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": "rds-db:connect",
"Resource": "arn:aws:rds-db:us-east-1:123456789012:dbuser:db-ABCDEFGHIJKL01234/db_user1"
}
]
}
A
The action 'rds-db:connect' is not allowed for RDS MySQL.
Why wrong: The action is correct for IAM database authentication.
B
The policy should have 'Deny' effect instead of 'Allow'.
Why wrong: Allow is correct for granting access.
C
The resource ARN in the policy uses an incorrect RDS resource ID.
The RDS resource ID must be exactly 14 alphanumeric characters. The example has 18.
D
The database user name in the ARN must be 'admin', not 'db_user1'.
Why wrong: The user name should match the database user.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The resource ARN in the policy uses an incorrect RDS resource ID.
Option C is correct because IAM database authentication for RDS MySQL requires the resource ARN in the IAM policy to include the correct RDS resource ID (the 'db-xxxxx' identifier from the RDS console), not the DB instance name or endpoint. If the ARN uses an incorrect resource ID, the policy will not match the target RDS instance, causing the authentication to fail even if the user name and action are correct.
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 action 'rds-db:connect' is not allowed for RDS MySQL.
Why it's wrong here
The action is correct for IAM database authentication.
✗
The policy should have 'Deny' effect instead of 'Allow'.
Why it's wrong here
Allow is correct for granting access.
✓
The resource ARN in the policy uses an incorrect RDS resource ID.
Why this is correct
The RDS resource ID must be exactly 14 alphanumeric characters. The example has 18.
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 database user name in the ARN must be 'admin', not 'db_user1'.
Why it's wrong here
The user name should match the database user.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the DB instance name or endpoint with the RDS resource ID, or assume the database user must be 'admin' for IAM authentication, when in fact the resource ID is a separate identifier and the user name must match the database user exactly.
Detailed technical explanation
How to think about this question
IAM database authentication for RDS MySQL uses an authentication token generated via the AWS CLI or SDK, which is sent to the database instead of a password. The token is validated against the IAM policy's resource ARN, which must follow the format 'arn:aws:rds-db:region:account-id:dbuser:db-resource-id/database-user-name'. If the resource ID (the 'db-xxxxx' string) is incorrect, the token validation fails, even if the IAM role and database user are correctly configured. This is a common misconfiguration when copying ARNs from the console or using the DB instance name instead of the resource ID.
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.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The resource ARN in the policy uses an incorrect RDS resource ID. — Option C is correct because IAM database authentication for RDS MySQL requires the resource ARN in the IAM policy to include the correct RDS resource ID (the 'db-xxxxx' identifier from the RDS console), not the DB instance name or endpoint. If the ARN uses an incorrect resource ID, the policy will not match the target RDS instance, causing the authentication to fail even if the user name and action are correct.
What should I do if I get this DBS-C01 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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