The answer is that the EBS volume creation failure triggered a stack rollback, which cancelled the previously successful EC2 instance creation. In CloudFormation, when any resource creation fails during stack creation, the service automatically initiates a rollback to undo all successfully created resources, returning the stack to its initial state. The 'Resource creation cancelled' error for the EC2 instance does not indicate a failure of the instance itself, but rather that it was terminated as part of the rollback process after the subsequent EBS volume failed. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of CloudFormation's dependency-aware rollback behavior and the distinction between a resource creation failure and a rollback cancellation. A common trap is misreading the event order—candidates often assume the EC2 instance failed first, when in reality it was undone retroactively. Memory tip: think "cancelled after creation" means rollback, not failure—the EBS volume is the root cause, the instance is just collateral damage.
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.
A company has a CloudFormation stack that creates an EC2 instance with a custom AMI. The stack fails with the error 'Resource creation cancelled' during creation. The engineer checks the stack events and sees that the EC2 instance creation succeeded, but the subsequent creation of an EBS volume failed. What is the MOST likely reason for the 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The EBS volume creation failed, causing the stack to roll back and cancel the instance
Option C is correct because when an EBS volume creation fails in a CloudFormation stack, the stack initiates a rollback of all previously created resources, including the EC2 instance. The 'Resource creation cancelled' error appears for the EC2 instance because its creation was successful but then undone during the rollback, not because it failed initially.
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 EC2 instance creation failed and then was cancelled
Why it's wrong here
The events show the instance creation succeeded.
✗
The EC2 instance had a DeletionPolicy of Retain, which prevented rollback
Why it's wrong here
A Retain policy would keep the instance, but the error is about creation cancellation.
✓
The EBS volume creation failed, causing the stack to roll back and cancel the instance
Why this is correct
If a subsequent resource fails, CloudFormation cancels previously created resources during rollback.
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 EC2 instance depended on the EBS volume, and the dependency caused a timeout
Why it's wrong here
Dependencies do not cause 'Resource creation cancelled' on a successful resource.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates misinterpret 'Resource creation cancelled' as a creation failure of the EC2 instance itself, rather than understanding it is a rollback cancellation of a previously successful resource.
Trap categories for this question
Command / output trap
The events show the instance creation succeeded.
Detailed technical explanation
How to think about this question
CloudFormation uses a sequential resource creation order based on dependencies defined in the DependsOn attribute or implicit references. During a rollback, CloudFormation deletes resources in reverse order of creation, and the 'Resource creation cancelled' status is a specific state indicating the resource was successfully created but then removed as part of the rollback. This behavior is distinct from a creation failure, which would show a 'CREATE_FAILED' status.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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.
Operations and Maintenance — This question tests Operations and Maintenance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The EBS volume creation failed, causing the stack to roll back and cancel the instance — Option C is correct because when an EBS volume creation fails in a CloudFormation stack, the stack initiates a rollback of all previously created resources, including the EC2 instance. The 'Resource creation cancelled' error appears for the EC2 instance because its creation was successful but then undone during the rollback, not because it failed initially.
What should I do if I get this PAS-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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Question Discussion
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