- A
The deployment failed because the ECS service was using the rolling update deployment controller. Change to blue/green deployment.
Why wrong: Rolling update is not the cause; circuit breaker is needed for automatic rollback.
- B
The deployment failed because the ECS service did not have the deployment circuit breaker enabled. Enable the circuit breaker with rollback.
The circuit breaker detects failed tasks and rolls back to the stable version, maintaining service availability.
- C
The deployment failed because the desired count was too low. Increase the desired count to 6.
Why wrong: Desired count does not prevent deployment failure from misconfiguration.
- D
The deployment failed because the health check grace period was too short. Increase the grace period.
Why wrong: Health check grace period affects health checks, not task startup failures.
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud solutions. 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 runs a critical microservice on Amazon ECS with AWS Fargate. The service must be highly available across multiple Availability Zones. The DevOps engineer configured the service with a desired count of 4 tasks spread across 2 Availability Zones. During a deployment, a new task fails to start due to a missing environment variable. The deployment fails, but the old tasks continue to run. What is the most likely cause of the deployment failure and how can the engineer ensure future deployments are resilient?
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 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 deployment failed because the ECS service did not have the deployment circuit breaker enabled. Enable the circuit breaker with rollback.
The deployment failed because the new task could not start due to a missing environment variable, and the ECS service did not have the deployment circuit breaker enabled. Without the circuit breaker, ECS continues to attempt the deployment indefinitely or until a timeout, but it does not automatically roll back to the previous stable task set. Enabling the deployment circuit breaker with rollback ensures that if a specified number of tasks fail to start (e.g., due to health checks or runtime errors), ECS automatically rolls back to the last successful deployment, maintaining service availability.
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 deployment failed because the ECS service was using the rolling update deployment controller. Change to blue/green deployment.
Why it's wrong here
Rolling update is not the cause; circuit breaker is needed for automatic rollback.
- ✓
The deployment failed because the ECS service did not have the deployment circuit breaker enabled. Enable the circuit breaker with rollback.
Why this is correct
The circuit breaker detects failed tasks and rolls back to the stable version, maintaining service availability.
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 deployment failed because the desired count was too low. Increase the desired count to 6.
Why it's wrong here
Desired count does not prevent deployment failure from misconfiguration.
- ✗
The deployment failed because the health check grace period was too short. Increase the grace period.
Why it's wrong here
Health check grace period affects health checks, not task startup failures.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on the deployment controller type (rolling vs. blue/green) or task count, but the real issue is the lack of automatic rollback capability provided by the deployment circuit breaker, which is specifically designed to handle task startup failures during deployments.
Detailed technical explanation
How to think about this question
The ECS deployment circuit breaker monitors the number of tasks that fail to reach a healthy state during a deployment. When enabled with rollback, it triggers a rollback if the failure threshold (default 50% of desired count) is exceeded, automatically reverting to the previous task set. This is particularly important for critical services where a misconfigured task definition (e.g., missing environment variable, incorrect image) could otherwise cause a full deployment failure without automatic recovery.
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.
- →
Resilient Cloud Solutions — study guide chapter
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FAQ
Questions learners often ask
What does this DOP-C02 question test?
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The deployment failed because the ECS service did not have the deployment circuit breaker enabled. Enable the circuit breaker with rollback. — The deployment failed because the new task could not start due to a missing environment variable, and the ECS service did not have the deployment circuit breaker enabled. Without the circuit breaker, ECS continues to attempt the deployment indefinitely or until a timeout, but it does not automatically roll back to the previous stable task set. Enabling the deployment circuit breaker with rollback ensures that if a specified number of tasks fail to start (e.g., due to health checks or runtime errors), ECS automatically rolls back to the last successful deployment, maintaining service availability.
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.
About these practice questions
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Last reviewed: Jun 24, 2026
This DOP-C02 practice question is part of Courseiva's free Amazon Web Services 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 DOP-C02 exam.
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