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SDLC Automation →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the rollback fails because the original task set’s desired count was set to zero during the blue/green deployment, and CodeDeploy cannot restore it if the original task definition or service configuration is no longer valid. During a blue/green deployment on ECS, CodeDeploy scales the original (blue) task set’s desired count down to zero after the new (green) task set is fully healthy, so when a rollback triggers, it attempts to scale that original task set back up—but if the original task definition has been deregistered or the service’s launch type has changed, the rollback has no valid configuration to reinstate. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of how CodeDeploy manages task set lifecycles and the specific failure mode when a rollback tries to revive a scaled-to-zero original set. A common trap is assuming the issue is with target group deregistration or CloudFormation, but the core problem is that the original task definition is no longer available to scale from zero. Memory tip: “Zero to hero fails if the recipe is gone”—the original task definition is the recipe CodeDeploy needs to scale the task set back up.

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 company is using AWS CodeDeploy with a blue/green deployment strategy for an Amazon ECS service. After a deployment, the new task set fails health checks, and CodeDeploy automatically rolls back to the original task set. However, the rollback fails because the original task set's desired count is set to 0. 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.

Question 1hardmultiple choice

Full question →

A
The original task set's desired count was set to 0 during the blue/green deployment and the rollback is unable to restore it because the original task definition is no longer available.
In blue/green deployments, the original task set is scaled down to 0. If the original task definition is deleted or replaced, rollback fails.
B
The original task set's health checks are failing.
Why wrong: Health checks failing would not set desired count to 0; the issue is with the new task set failing health checks.
C
The original task set's CloudFormation stack was deleted during the deployment.
Why wrong: CodeDeploy does not delete CloudFormation stacks; it manages ECS services directly.
D
The original task set was deregistered from the target group.
Why wrong: Deregistration from target group would not cause the desired count to be 0; it's about routing traffic.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The original task set's desired count was set to 0 during the blue/green deployment and the rollback is unable to restore it because the original task definition is no longer available.

Option D is correct because during a blue/green deployment, the original task set's desired count is often scaled down to zero, and rollback tries to restore it but may fail if the original task definition or service configuration is no longer valid. Option A is wrong because CodeDeploy manages ECS service updates, not through CloudFormation. Option B is wrong because the issue is not about deregistering from the target group; it's about scaling. Option C is wrong because health checks are failing on the new task set, not the original.

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 original task set's desired count was set to 0 during the blue/green deployment and the rollback is unable to restore it because the original task definition is no longer available.
Why this is correct
In blue/green deployments, the original task set is scaled down to 0. If the original task definition is deleted or replaced, rollback fails.
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 original task set's health checks are failing.
Why it's wrong here
Health checks failing would not set desired count to 0; the issue is with the new task set failing health checks.
✗
The original task set's CloudFormation stack was deleted during the deployment.
Why it's wrong here
CodeDeploy does not delete CloudFormation stacks; it manages ECS services directly.
✗
The original task set was deregistered from the target group.
Why it's wrong here
Deregistration from target group would not cause the desired count to be 0; it's about routing traffic.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

What to study next

Got this wrong? Here's your next step.

Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

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 original task set's desired count was set to 0 during the blue/green deployment and the rollback is unable to restore it because the original task definition is no longer available. — Option D is correct because during a blue/green deployment, the original task set's desired count is often scaled down to zero, and rollback tries to restore it but may fail if the original task definition or service configuration is no longer valid. Option A is wrong because CodeDeploy manages ECS service updates, not through CloudFormation. Option B is wrong because the issue is not about deregistering from the target group; it's about scaling. Option C is wrong because health checks are failing on the new task set, not the original.

What should I do if I get this DOP-C02 question wrong?

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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