The most likely cause is that the IAM policy’s resource ARN specifies a specific region (us-east-1), but the target EC2 instances reside in a different region. This is because the `Resource` element in the policy statement explicitly restricts the `ec2:StartInstances` and `ec2:StopInstances` actions to instances with ARNs matching `arn:aws:ec2:us-east-1:123456789012:instance/*`, so any attempt to start or stop instances in another region will be denied by AWS’s implicit deny. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of how region-specific ARNs in IAM policies create unintended permission boundaries, especially when SAP automation scripts or lifecycle hooks assume a role that must operate across regions. A common trap is to overlook the region component in the ARN and assume the wildcard covers all resources. Memory tip: “ARN region locks your action—check the region before you start or stop.”
PAS-C01 Operations and Maintenance Practice Question
This PAS-C01 practice question tests your understanding of operations and maintenance. 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 is attached to a role used by an EC2 instance running SAP. The instance is unable to start or stop other EC2 instances. 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.
The policy does not allow `ec2:RebootInstances` which is required to start instances.
Why wrong: Reboot is not required for start/stop.
B
The policy does not include `iam:PassRole` permission.
Why wrong: PassRole is needed to associate an instance profile, but not for starting/stopping existing instances.
C
The policy does not include `ec2:DescribeInstances` for instances in other regions.
Why wrong: The policy allows DescribeInstances on all instances? Actually, the resource is limited to us-east-1, so DescribeInstances would also be limited.
D
The policy resource ARN specifies a specific region (us-east-1), but the instances are in a different region.
The resource ARN 'arn:aws:ec2:us-east-1:123456789012:instance/*' restricts the policy to instances in us-east-1 only.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The policy resource ARN specifies a specific region (us-east-1), but the instances are in a different region.
The policy allows `ec2:StartInstances` and `ec2:StopInstances` on all resources (`"Resource": "*"`), so it should work. However, the condition is missing. The issue could be that the policy does not include the `ec2:DescribeInstanceStatus` action needed to check status before starting/stopping. But the question says it cannot start/stop; the policy seems correct. Actually, the most likely cause is that the role does not have permission to pass the instance profile (iam:PassRole) if the instance uses an instance profile, but that is not shown. Alternatively, the policy is missing `ec2:DescribeInstances` which is needed for the AWS CLI to list instances? But it is included. Let's think: The policy allows start/stop on all resources, so it should work. Possibly the issue is that the EC2 instance has an instance profile that the role cannot pass. But the question says the policy is attached to the role; the role is used by the instance. The policy looks correct. However, the exhibit might be missing the `ec2:DescribeInstanceStatus` action, but that is not required for start/stop. I'll choose option C: The policy does not include `ec2:DescribeInstances` for the specific instances? No, it's there. Actually, the correct answer is that the policy does not include `ec2:DescribeInstances` for the instances? It does. Hmm. Let's look at the options: A) The policy does not allow `ec2:StartInstances` on specific instance IDs. B) The policy does not include `ec2:DescribeInstances` for the instances. C) The policy does not include `ec2:RebootInstances`. D) The policy does not allow `s3:GetObject` on the backup bucket. None of these are correct. I need to adjust the exhibit to make the question work. Let me modify the exhibit to include a condition that restricts the resource to only certain instances. For example:
```
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"ec2:DescribeInstances",
"ec2:StartInstances",
"ec2:StopInstances",
"ec2:RebootInstances"
],
"Resource": "arn:aws:ec2:us-east-1:123456789012:instance/*"
},
{
"Effect": "Allow",
"Action": [
"s3:GetObject",
"s3:PutObject"
],
"Resource": "arn:aws:s3:::sap-backup-bucket/*"
}
]
}
```
Then the question: The instance is unable to start or stop instances in another region. Why? Because the resource ARN specifies us-east-1, but the instances are in eu-west-1. That is plausible. I'll use that.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 `ec2:RebootInstances` which is required to start instances.
Why it's wrong here
Reboot is not required for start/stop.
✗
The policy does not include `iam:PassRole` permission.
Why it's wrong here
PassRole is needed to associate an instance profile, but not for starting/stopping existing instances.
✗
The policy does not include `ec2:DescribeInstances` for instances in other regions.
Why it's wrong here
The policy allows DescribeInstances on all instances? Actually, the resource is limited to us-east-1, so DescribeInstances would also be limited.
✓
The policy resource ARN specifies a specific region (us-east-1), but the instances are in a different region.
Why this is correct
The resource ARN 'arn:aws:ec2:us-east-1:123456789012:instance/*' restricts the policy to instances in us-east-1 only.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PAS-C01 NAT questions on configuration and troubleshooting.
Operations and Maintenance — This question tests Operations and Maintenance — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The policy resource ARN specifies a specific region (us-east-1), but the instances are in a different region. — The policy allows `ec2:StartInstances` and `ec2:StopInstances` on all resources (`"Resource": "*"`), so it should work. However, the condition is missing. The issue could be that the policy does not include the `ec2:DescribeInstanceStatus` action needed to check status before starting/stopping. But the question says it cannot start/stop; the policy seems correct. Actually, the most likely cause is that the role does not have permission to pass the instance profile (iam:PassRole) if the instance uses an instance profile, but that is not shown. Alternatively, the policy is missing `ec2:DescribeInstances` which is needed for the AWS CLI to list instances? But it is included. Let's think: The policy allows start/stop on all resources, so it should work. Possibly the issue is that the EC2 instance has an instance profile that the role cannot pass. But the question says the policy is attached to the role; the role is used by the instance. The policy looks correct. However, the exhibit might be missing the `ec2:DescribeInstanceStatus` action, but that is not required for start/stop. I'll choose option C: The policy does not include `ec2:DescribeInstances` for the specific instances? No, it's there. Actually, the correct answer is that the policy does not include `ec2:DescribeInstances` for the instances? It does. Hmm. Let's look at the options: A) The policy does not allow `ec2:StartInstances` on specific instance IDs. B) The policy does not include `ec2:DescribeInstances` for the instances. C) The policy does not include `ec2:RebootInstances`. D) The policy does not allow `s3:GetObject` on the backup bucket. None of these are correct. I need to adjust the exhibit to make the question work. Let me modify the exhibit to include a condition that restricts the resource to only certain instances. For example:
```
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"ec2:DescribeInstances",
"ec2:StartInstances",
"ec2:StopInstances",
"ec2:RebootInstances"
],
"Resource": "arn:aws:ec2:us-east-1:123456789012:instance/*"
},
{
"Effect": "Allow",
"Action": [
"s3:GetObject",
"s3:PutObject"
],
"Resource": "arn:aws:s3:::sap-backup-bucket/*"
}
]
}
```
Then the question: The instance is unable to start or stop instances in another region. Why? Because the resource ARN specifies us-east-1, but the instances are in eu-west-1. That is plausible. I'll use that.
What should I do if I get this PAS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PAS-C01 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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