DOP-C02 Resilient Cloud Solutions Practice Question
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?
⚠ Common exam trap
It's easy for candidates to 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.
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 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.
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 the CodeDeploy deployment group were associated with a different ECS service, the deployment would either fail during initial validation or target the wrong task set, preventing the green tasks from being provisioned at all. Since the deployment successfully schedules and starts the green tasks, the service association is confirmed correct, and this is not the reason traffic isn't being routed.
- ✓
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
In CodeDeploy's ECS blue/green deployment, the green target group's health checks are the gating mechanism for traffic shifting. If the health check path, port, or interval is misconfigured, the green tasks are marked unhealthy even though the containerized application is running normally, so CodeDeploy never receives the signal that the green fleet is ready. As a result, the listener remains pointed at the blue target group, and the deployment times out waiting for a healthy green target.
- ✗
The blue target group is still set as the production target group in the load balancer listener.
Why it's wrong here
CodeDeploy's ECS blue/green deployment automatically modifies the load balancer listener rules to shift production traffic from the blue target group to the green target group, and it does so gradually based on the deployment configuration. The blue target group is intentionally retained for rollback purposes, but it is not left as the active production target after the shift begins; if the listener still routed to blue, that would mean the traffic shift never occurred, which contradicts the deployment's progress.
- ✗
The green tasks are in a different VPC than the load balancer.
Why it's wrong here
ECS tasks and the Application Load Balancer must reside in the same VPC for the tasks to register with the green target group; if they were in different VPCs, the target group registration would fail immediately, causing the deployment to error out before reaching the traffic-routing phase. Since the green tasks are running and CodeDeploy is waiting to shift traffic, the VPC configuration is valid, and this is not why traffic isn't being routed.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.