The answer is an invalid or deregistered AMI ID. CloudFormation stack creation fails and rolls back when the specified AMI ID cannot be used to launch an EC2 instance, because the service validates the AMI during resource provisioning—if the ID is mistyped, belongs to a different AWS region, or has been deregistered, the instance launch fails and triggers a stack rollback. On the CompTIA Cloud+ CV0-004 exam, this scenario tests your understanding of template portability errors, a common trap when copying CloudFormation templates between regions without updating region-specific AMI IDs. Remember that AMI IDs are region-specific and can change when an AMI owner deregisters the image, so always verify the ID before deployment. A helpful memory tip: “AMI IDs are regional—copy the template, but not the ID.”
CV0-004 Deployment Practice Question
This CV0-004 practice question tests your understanding of deployment. 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
StackStatus: "ROLLBACK_IN_PROGRESS"
StackEvents:
- ResourceStatus: "CREATE_FAILED"
ResourceType: "AWS::EC2::Instance"
ResourceStatusReason: "Value of property ImageId is invalid. Please use a valid AMI."
Refer to the exhibit. A cloud administrator launched a CloudFormation stack to deploy an EC2 instance, but the stack is rolling back. 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.
StackStatus: "ROLLBACK_IN_PROGRESS"
StackEvents:
- ResourceStatus: "CREATE_FAILED"
ResourceType: "AWS::EC2::Instance"
ResourceStatusReason: "Value of property ImageId is invalid. Please use a valid AMI."
A
The security group referenced in the template does not exist.
Why wrong: A missing security group would produce an error about the security group, not ImageId.
B
The subnet ID is in a different VPC.
Why wrong: A subnet mismatch would produce an error about subnet or VPC, not ImageId.
C
The AMI ID is invalid or has been deregistered.
The error directly states 'ImageId is invalid', so the AMI ID is incorrect or no longer exists.
D
The instance type is not available in the selected region.
Why wrong: The error mentions ImageId, not instance type; an unsupported instance type would give a different error.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The AMI ID is invalid or has been deregistered.
Option C is correct because CloudFormation validates the AMI ID during stack creation. If the AMI ID is invalid (e.g., mistyped, belongs to a different region, or has been deregistered), the EC2 instance launch fails, causing CloudFormation to roll back the stack. This is a common misconfiguration when copying templates across regions without updating AMI IDs.
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 security group referenced in the template does not exist.
Why it's wrong here
A missing security group would produce an error about the security group, not ImageId.
✗
The subnet ID is in a different VPC.
Why it's wrong here
A subnet mismatch would produce an error about subnet or VPC, not ImageId.
✓
The AMI ID is invalid or has been deregistered.
Why this is correct
The error directly states 'ImageId is invalid', so the AMI ID is incorrect or no longer exists.
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 instance type is not available in the selected region.
Why it's wrong here
The error mentions ImageId, not instance type; an unsupported instance type would give a different error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a missing security group or wrong subnet causes rollbacks, but CloudFormation performs upfront validation for those parameters, whereas an invalid AMI ID is only detected at launch time, making it the most likely cause of a rollback.
Detailed technical explanation
How to think about this question
CloudFormation stack rollbacks occur when a resource creation fails after the stack has begun provisioning. For EC2 instances, the launch process involves calling the RunInstances API, which checks the AMI's state (available, pending, or deregistered) and region compatibility. If the AMI is deregistered, the API returns an 'InvalidAMIID.NotFound' error, causing CloudFormation to mark the resource as CREATE_FAILED and initiate a rollback. This differs from validation errors (e.g., missing security group) that prevent the stack from even starting.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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.
Deployment — This question tests Deployment — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The AMI ID is invalid or has been deregistered. — Option C is correct because CloudFormation validates the AMI ID during stack creation. If the AMI ID is invalid (e.g., mistyped, belongs to a different region, or has been deregistered), the EC2 instance launch fails, causing CloudFormation to roll back the stack. This is a common misconfiguration when copying templates across regions without updating AMI IDs.
What should I do if I get this CV0-004 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.
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 →
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 cloud administrator is debugging a failed CloudFormation stack creation. The exhibit shows the stack events. What is the most likely cause of the failure?
medium
A.The instance type is not supported in the region.
B.The stack name already exists.
C.The AMI ID is incorrect.
✓ D.The referenced security group does not exist in the chosen VPC.
Why D: The stack creation fails with a 'CREATE_FAILED' status on the security group resource, and the error message indicates that the security group does not exist in the specified VPC. This is a common issue when a CloudFormation template references a security group by ID or name that is not present in the target VPC, causing the resource creation to fail. The stack events show the security group resource as the point of failure, confirming that the referenced security group is missing.
Last reviewed: Jun 25, 2026
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This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.
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