The answer is that the CloudFormation stack already exists in a previous failed state, specifically ROLLBACK_COMPLETE or UPDATE_ROLLBACK_COMPLETE. This is correct because CloudFormation treats a stack in a failed state as immutable for further updates; any attempt to update it—such as from a CodePipeline deploy action—is rejected by the service, causing the pipeline deployment to fail. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of CloudFormation stack lifecycle states and how CodePipeline’s deploy action interacts with them. A common trap is assuming a failed stack can simply be retried, but the key is that CloudFormation requires manual intervention—either deleting the stack or continuing the rollback—before a new update can proceed. Memory tip: think of a failed stack as a locked door; you cannot push it open again until you either remove the door (delete) or turn the handle (continue rollback).
DOP-C02 SDLC Automation Practice Question
This DOP-C02 practice question tests your understanding of sdlc automation. 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 team uses AWS CodePipeline to deploy a microservices application. The pipeline has a deploy action that uses AWS CloudFormation. The CloudFormation template creates an Amazon ECS service. The deployment fails because the ECS service cannot be updated. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The CloudFormation stack already exists and is in a previous failed state.
When a CloudFormation stack update fails, the stack enters a ROLLBACK_COMPLETE or UPDATE_ROLLBACK_COMPLETE state. In this state, the stack is considered to be in a 'failed' state and cannot be updated again until it is either deleted or the stack is manually continued with a rollback. CodePipeline's CloudFormation deploy action will attempt to perform a stack update, but CloudFormation rejects the request because the existing stack is in a non-updatable state, causing the pipeline deployment to fail.
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 CloudFormation stack already exists and is in a previous failed state.
Why this is correct
A failed stack must be deleted or updated with a changeset.
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 ECS service is in a steady state and cannot be modified.
Why it's wrong here
ECS services can be updated even when running.
✗
The CodePipeline deploy action is configured with the wrong action type.
Why it's wrong here
The action type being correct is not the root cause.
✗
The IAM role used by CloudFormation does not have permission to update ECS services.
Why it's wrong here
This would cause an authorization error, but not specifically an update failure.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the error is due to missing IAM permissions or a misconfigured action type, but the real issue is CloudFormation's requirement that stacks be in a valid state before updates can proceed.
Detailed technical explanation
How to think about this question
CloudFormation stack updates are atomic and require the stack to be in a stable state (CREATE_COMPLETE, UPDATE_COMPLETE, or UPDATE_ROLLBACK_COMPLETE). A stack in ROLLBACK_COMPLETE is considered 'failed' and cannot be updated; you must first execute a ContinueUpdateRollback API call or delete the stack. This is a common pitfall in CI/CD pipelines where a previous failed deployment leaves the stack in a stuck state, blocking subsequent updates until manual intervention.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
SDLC Automation — This question tests SDLC Automation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The CloudFormation stack already exists and is in a previous failed state. — When a CloudFormation stack update fails, the stack enters a ROLLBACK_COMPLETE or UPDATE_ROLLBACK_COMPLETE state. In this state, the stack is considered to be in a 'failed' state and cannot be updated again until it is either deleted or the stack is manually continued with a rollback. CodePipeline's CloudFormation deploy action will attempt to perform a stack update, but CloudFormation rejects the request because the existing stack is in a non-updatable state, causing the pipeline deployment to fail.
What should I do if I get this DOP-C02 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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