This PAS-C01 practice question tests your understanding of technology. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. A key principle to apply: iAM Role Trust Policy. 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.
An SAP administrator uses an IAM role attached to an EC2 instance to perform backups. The backup script fails when trying to write to an S3 bucket and create EBS snapshots. 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 S3 bucket policy denies all writes from this role.
Why wrong: Incorrect. While a bucket policy denying writes would cause S3 failures, it does not affect EBS snapshots, so it cannot explain both failures.
B
The trust policy does not include the EC2 service principal.
Correct. Without the EC2 service principal in the trust policy, the instance cannot assume the role, causing all API calls to fail.
C
The role does not have permission to create snapshots due to an explicit deny.
Why wrong: Incorrect. An explicit deny for ec2:CreateSnapshot would only affect snapshots, not S3 writes.
D
The policy lacks 's3:ListBucket' and 'ec2:CreateSnapshot' requires volume ARN.
Why wrong: Incorrect. s3:ListBucket is not required for writing objects; only s3:PutObject is needed. The volume ARN requirement for ec2:CreateSnapshot can be satisfied with a wildcard.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The trust policy does not include the EC2 service principal.
The most likely cause is that the trust policy of the IAM role does not include the EC2 service principal (ec2.amazonaws.com). Without this, the EC2 instance cannot assume the role, causing all AWS API calls from the backup script to fail, including writing to S3 and creating EBS snapshots. Options A and C only affect specific actions, and D incorrectly includes s3:ListBucket as a requirement.
Key principle: IAM Role Trust Policy
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 S3 bucket policy denies all writes from this role.
Why it's wrong here
Incorrect. While a bucket policy denying writes would cause S3 failures, it does not affect EBS snapshots, so it cannot explain both failures.
✓
The trust policy does not include the EC2 service principal.
Why this is correct
Correct. Without the EC2 service principal in the trust policy, the instance cannot assume the role, causing all API calls to fail.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
IAM Role Trust Policy
✗
The role does not have permission to create snapshots due to an explicit deny.
Why it's wrong here
Incorrect. An explicit deny for ec2:CreateSnapshot would only affect snapshots, not S3 writes.
✗
The policy lacks 's3:ListBucket' and 'ec2:CreateSnapshot' requires volume ARN.
Why it's wrong here
Incorrect. s3:ListBucket is not required for writing objects; only s3:PutObject is needed. The volume ARN requirement for ec2:CreateSnapshot can be satisfied with a wildcard.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates often focus on missing S3 or EC2 permissions but overlook the prerequisite trust policy. If the instance cannot assume the role, no permissions are applied.
Detailed technical explanation
How to think about this question
For `ec2:CreateSnapshot`, the resource element must specify the volume ARN (e.g., `arn:aws:ec2:region:account-id:volume/vol-xxx`) to satisfy the condition key `ec2:Volume`; using a wildcard without the volume ARN will cause an implicit deny. Similarly, `s3:ListBucket` is required for operations like `PutObject` because the S3 API first checks bucket-level permissions before object-level actions. In real-world scenarios, missing these specific permissions is a common misconfiguration when attaching managed policies that lack resource-level constraints.
KKey Concepts to Remember
IAM Role Trust Policy
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
IAM Role Trust Policy
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.
Quick reference
AWS S3 Storage Class Comparison
Storage Class
Min Duration
Retrieval
Use Case
S3 Standard
None
Immediate
Frequently accessed data
S3 Standard-IA
30 days
Immediate
Infrequent access, rapid retrieval
S3 One Zone-IA
30 days
Immediate
Non-critical infrequent data
S3 Intelligent-Tiering
None
Immediate–hours
Unknown or changing access patterns
S3 Glacier Instant
90 days
Milliseconds
Archive with instant retrieval
S3 Glacier Flexible
90 days
Minutes–hours
Archive, flexible retrieval
S3 Glacier Deep Archive
180 days
Hours
Long-term compliance archive
What to study next
Got this wrong? Here's your next step.
Review iAM Role Trust Policy, then practise related PAS-C01 questions on the same topic to reinforce the concept.
Technology — This question tests Technology — IAM Role Trust Policy.
What is the correct answer to this question?
The correct answer is: The trust policy does not include the EC2 service principal. — The most likely cause is that the trust policy of the IAM role does not include the EC2 service principal (ec2.amazonaws.com). Without this, the EC2 instance cannot assume the role, causing all AWS API calls from the backup script to fail, including writing to S3 and creating EBS snapshots. Options A and C only affect specific actions, and D incorrectly includes s3:ListBucket as a requirement.
What should I do if I get this PAS-C01 question wrong?
Review iAM Role Trust Policy, then practise related PAS-C01 questions on the same topic to reinforce the concept.
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?
IAM Role Trust Policy
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