The answer is a misconfigured health check on the green target group. CodeDeploy’s blue/green deployment for ECS relies on the green target group’s health check to validate that the new tasks are ready to receive traffic before shifting any load. Even if the green tasks themselves are running and passing their own container health checks, a misconfigured target group health check—such as an incorrect path, port, or protocol—will cause CodeDeploy to mark the entire green fleet as unhealthy. With a 'Linear10PercentEvery3Minutes' traffic shifting configuration, CodeDeploy will not begin shifting traffic until the green target group reports a healthy status; if it never does, the green tasks remain at zero traffic. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding that CodeDeploy decouples task-level health from target group health, and the common trap is assuming that passing ECS health checks guarantees traffic routing. Remember: green tasks need a green light from the load balancer, not just from ECS.
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 application on Amazon ECS with the Fargate launch type. The application is deployed across three Availability Zones. Each service has its own Application Load Balancer. The company wants to implement a blue/green deployment strategy to reduce risk. They currently use AWS CodeDeploy for ECS deployments. During a recent deployment, the company noticed that the new version (green) was not receiving any traffic even after passing all health checks. The CodeDeploy configuration uses a 'Linear10PercentEvery3Minutes' traffic shifting configuration. What is the most likely reason that the green tasks are not receiving traffic?
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 green target group's health check is misconfigured, causing CodeDeploy to consider the green tasks unhealthy and not route traffic.
The green target group's health check is misconfigured, causing CodeDeploy to consider the green tasks unhealthy. With a 'Linear10PercentEvery3Minutes' traffic shifting configuration, CodeDeploy gradually shifts traffic in 10% increments every 3 minutes, but only if the green target group passes health checks. If the health check fails, CodeDeploy stops traffic shifting, leaving the green tasks with zero traffic despite the tasks themselves being healthy.
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 CodeDeploy deployment group is not associated with the correct ECS service.
Why it's wrong here
If it were incorrect, the deployment would not proceed at all.
✓
The green target group's health check is misconfigured, causing CodeDeploy to consider the green tasks unhealthy and not route traffic.
Why this is correct
Health check failures prevent traffic routing even if tasks run.
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 blue target group is still set as the production target group in the load balancer listener.
Why it's wrong here
CodeDeploy updates the listener to route traffic to the green target group gradually.
✗
The green tasks are in a different VPC than the load balancer.
Why it's wrong here
Tasks and load balancer must be in the same VPC; otherwise deployment fails.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume health checks passing on the ECS tasks means traffic will automatically route, but CodeDeploy relies on the target group's health check configuration, not the task's health status, to determine when to shift traffic.
Detailed technical explanation
How to think about this question
CodeDeploy uses the 'test' and 'prod' target group concept for blue/green deployments. The green target group is initially the 'test' target group, and traffic is shifted by modifying the ALB listener's default action to forward traffic to the green target group in increments. If the health check on the green target group fails—even if the tasks are healthy—CodeDeploy treats the deployment as failed and stops shifting traffic, leaving the blue target group as the active target. Health checks are configured on the target group, not on the ECS task definition, so a misconfigured health check path, port, or protocol can cause this behavior.
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.
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 green target group's health check is misconfigured, causing CodeDeploy to consider the green tasks unhealthy and not route traffic. — The green target group's health check is misconfigured, causing CodeDeploy to consider the green tasks unhealthy. With a 'Linear10PercentEvery3Minutes' traffic shifting configuration, CodeDeploy gradually shifts traffic in 10% increments every 3 minutes, but only if the green target group passes health checks. If the health check fails, CodeDeploy stops traffic shifting, leaving the green tasks with zero traffic despite the tasks themselves being healthy.
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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