Question 938 of 1,663
RDS IAM Policy Deny Override
Exhibit
Refer to the exhibit.
```
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"rds:DescribeDBInstances",
"rds:ModifyDBInstance"
],
"Resource": "*"
},
{
"Effect": "Deny",
"Action": "rds:ModifyDBInstance",
"Resource": "arn:aws:rds:us-east-1:123456789012:db:prod-db"
}
]
}
```A company attaches the above IAM policy to a user. The user tries to modify the DB instance 'prod-db' in us-east-1. What is the result?
Quick Answer
The answer is that the user cannot modify prod-db. This outcome occurs because an explicit deny in an RDS IAM policy always overrides any allow, regardless of the order in which the statements appear. When AWS evaluates IAM policies, it defaults to an implicit deny for any action not explicitly allowed, but an explicit deny is a hard block that cannot be bypassed by a separate allow statement. On the AWS Certified Database Specialty DBS-C01 exam, this concept tests your understanding of IAM policy evaluation logic, specifically the priority of explicit denies over allows—a common trap is assuming the most specific or most recent statement wins. Remember that explicit deny is the ultimate override: it acts like a kill switch that no allow can flip back. Memory tip: “Deny is the final word—once denied, always denied.”
⚠ Common exam trap
Candidates often focus on the resource ARN in the Deny statement and miss that it is `"*"`, meaning it applies to all resources. They may think the Deny is scoped only to `prod-db` if they misread the policy.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The user cannot modify any DB instance.
The IAM policy includes an explicit Deny statement that denies the `rds:ModifyDBInstance` action on all resources (`Resource: "*"`). In AWS IAM, an explicit Deny overrides any Allow. Therefore, the user cannot modify any DB instance, including `prod-db`. Options A and B are incorrect because the user can describe DB instances (unless denied) and the Allow does not override the Deny. Option C is incorrect because the Deny applies to all instances, not just `prod-db`.
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 user cannot describe DB instances.
Why it's wrong here
The policy does not explicitly deny `rds:DescribeDBInstances`, so the user can describe DB instances unless there is another policy denying it. This option is incorrect.
- ✗
The user can modify prod-db because the Allow statement covers it.
Why it's wrong here
The Allow statement exists, but the explicit Deny overrides it. Therefore, the user cannot modify any DB instance. This option is incorrect.
- ✗
The user cannot modify prod-db.
Why it's wrong here
The user cannot modify any DB instance, not just `prod-db`, because the Deny uses `Resource: "*"`. This option is partially correct but incomplete; the correct answer is 'cannot modify any DB instance'.
- ✓
The user cannot modify any DB instance.
Why this is correct
The explicit Deny with `Resource: "*"` denies `rds:ModifyDBInstance` on all DB instances, so the user cannot modify any DB instance. This option is correct.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on DBS-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A DBA runs the IAM policy simulation above. The DBA can describe the DB instance but cannot modify it. What is the most likely cause?
medium- A.The resource ARN in the simulation is incorrect.
- ✓ B.An IAM policy explicitly denies the rds:ModifyDBInstance action.
- C.The DBA's IAM policy does not include an allow for rds:ModifyDBInstance.
- D.The DBA is not within the VPC where the DB instance resides.
Why B: The simulation shows that the DBA can describe the DB instance but cannot modify it. Since the simulation evaluates all applicable IAM policies, an explicit deny for rds:ModifyDBInstance in any attached policy will override any allow and cause the modify action to fail. This is the most likely cause because explicit denies are evaluated first and cannot be overridden by other policies.
Last reviewed: Jul 4, 2026
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.