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SDLC Automation →hardMultiple ChoiceObjective-mapped

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.

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 A is correct because during a blue/green deployment on ECS, CodeDeploy sets the original (blue) task set's desired count to 0 after the new (green) task set is created and begins serving traffic. If the green task set fails health checks and triggers an automatic rollback, CodeDeploy attempts to restore the original task set's desired count to its previous value. However, if the original task definition has been deregistered or deleted (e.g., due to lifecycle policies or manual cleanup), the rollback cannot scale the original task set back up, causing the rollback 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 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

The trap here is that candidates assume the rollback fails because the original task set is unhealthy or deregistered from the target group, when in reality the root cause is the deletion of the original task definition, which CodeDeploy needs to recreate the task set during rollback.

Detailed technical explanation

How to think about this question

Under the hood, CodeDeploy uses the ECS 'CreateTaskSet' and 'UpdateServicePrimaryTaskSet' APIs to manage blue/green deployments. The original task set's desired count is set to 0 via the 'UpdateService' API call, but the task set and its task definition remain registered in ECS. If the task definition is deleted (e.g., via 'DeregisterTaskDefinition' or lifecycle expiration), the rollback cannot reference it to create new tasks, leading to a 'TaskDefinition not found' error. This is a common pitfall when teams automate cleanup of old task definitions without considering rollback scenarios.

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

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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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 A is correct because during a blue/green deployment on ECS, CodeDeploy sets the original (blue) task set's desired count to 0 after the new (green) task set is created and begins serving traffic. If the green task set fails health checks and triggers an automatic rollback, CodeDeploy attempts to restore the original task set's desired count to its previous value. However, if the original task definition has been deregistered or deleted (e.g., due to lifecycle policies or manual cleanup), the rollback cannot scale the original task set back up, causing the rollback 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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