The answer is that the engineer lacks permissions to pass an IAM role to the DB instance during creation. When you use an IAM policy to allow `rds:CreateDBInstance`, the API call also requires the `iam:PassRole` action on any IAM role you specify for the instance, such as for automated backups or enhanced monitoring. Even if the policy correctly targets `arn:aws:rds:us-east-1:123456789012:db:prod-*`, the missing `iam:PassRole` permission blocks the operation entirely. On the AWS Certified Database Specialty DBS-C01 exam, this tests your understanding that RDS creation is a multi-step authorization—the policy must cover both the RDS resource and the IAM role resource. A common trap is focusing only on the DB identifier pattern while overlooking the role-passing requirement. Remember the mnemonic: “Create needs Pass” — for any `CreateDBInstance` call that includes a role, you must explicitly grant `iam:PassRole` on that role ARN.
DBS-C01 Management and Operations Practice Question
This DBS-C01 practice question tests your understanding of management and operations. 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
Refer to the exhibit.
Exhibit: IAM policy snippet
```json
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"rds:CreateDBInstance",
"rds:DeleteDBInstance",
"rds:ModifyDBInstance"
],
"Resource": "arn:aws:rds:us-east-1:123456789012:db:prod-*"
}
]
}
```
A database administrator is creating an IAM policy to allow a DevOps engineer to manage production RDS instances. The policy above is attached to the engineer's IAM role. The engineer reports that they cannot create a new DB instance with the identifier 'prod-analytics'. 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 engineer does not have permissions to pass an IAM role to the DB instance if one is specified.
The policy grants permissions to resources matching 'prod-*', but creating a DB instance requires the 'rds:CreateDBInstance' action on the 'arn:aws:rds:us-east-1:123456789012:db:prod-*' resource. However, the CreateDBInstance API call also requires permissions on other resources such as security groups, subnets, etc. But the error is likely because the policy does not allow the action on the specific resource, but the resource ARN matches. Actually, the most common issue is that the policy does not include 'rds:CreateDBInstance' on the 'aws:RequestTag' condition or the resource ARN pattern is incorrect. However, the policy looks correct for the resource. A common mistake is that the policy does not allow 'rds:CreateDBInstance' on the 'arn:aws:rds:us-east-1:123456789012:db:*' for creation, but the policy uses 'prod-*'. That should work. Another possibility is that the engineer is trying to create the instance in a different region or account. But the exhibit shows the policy is for 'us-east-1'. So the most likely reason is that the 'rds:CreateDBInstance' action requires additional permissions on other resources (like EC2 security groups) that are not granted.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 policy does not allow the 'rds:CreateDBInstance' action on the required resource because the resource ARN pattern is incorrect.
Why it's wrong here
The resource ARN pattern 'prod-*' matches 'prod-analytics'.
✗
The policy does not include the 'rds:CreateDBSecurityGroup' action.
Why it's wrong here
RDS uses security groups, not DBSecurityGroup (deprecated).
✓
The engineer does not have permissions to pass an IAM role to the DB instance if one is specified.
Why this is correct
When creating a DB instance with an IAM role, the 'iam:PassRole' permission is required. This is a common missing permission.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The policy does not include the 'rds:CreateDBInstance' action for all regions.
Why it's wrong here
The policy is scoped to us-east-1, which is where the engineer is likely operating.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Management and Operations — This question tests Management and Operations — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The engineer does not have permissions to pass an IAM role to the DB instance if one is specified. — The policy grants permissions to resources matching 'prod-*', but creating a DB instance requires the 'rds:CreateDBInstance' action on the 'arn:aws:rds:us-east-1:123456789012:db:prod-*' resource. However, the CreateDBInstance API call also requires permissions on other resources such as security groups, subnets, etc. But the error is likely because the policy does not allow the action on the specific resource, but the resource ARN matches. Actually, the most common issue is that the policy does not include 'rds:CreateDBInstance' on the 'aws:RequestTag' condition or the resource ARN pattern is incorrect. However, the policy looks correct for the resource. A common mistake is that the policy does not allow 'rds:CreateDBInstance' on the 'arn:aws:rds:us-east-1:123456789012:db:*' for creation, but the policy uses 'prod-*'. That should work. Another possibility is that the engineer is trying to create the instance in a different region or account. But the exhibit shows the policy is for 'us-east-1'. So the most likely reason is that the 'rds:CreateDBInstance' action requires additional permissions on other resources (like EC2 security groups) that are not granted.
What should I do if I get this DBS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DBS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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