- A
The lifecycle hooks for the new task set are failing.
Why wrong: Lifecycle hooks run before traffic is shifted; if they fail, the deployment would not proceed to traffic shift, so this does not match the described sequence.
- B
The target group for the new task set is not configured correctly.
Why wrong: Incorrect target group configuration might cause traffic routing issues, but it would not directly trigger a rollback; the deployment would likely complete with routing errors.
- C
The deployment group's rollback configuration triggers due to alarm threshold.
Why wrong: Rollback due to CloudWatch alarms is possible, but the scenario states the rollback happens 'after a few minutes' immediately after traffic shift, which is typical of post-traffic validation failure, not an alarm that takes time to evaluate.
- D
The new task set fails the post-traffic shift validation tests.
CodeDeploy performs validation after traffic shift; if the validation fails (e.g., health check failure or Lambda hook failure), it triggers an automatic rollback to the original task set.
Quick Answer
The answer is that the new task set fails the post-traffic shift validation tests. In an ECS blue/green deployment using CodeDeploy, after traffic is routed to the new task set, CodeDeploy executes post-traffic shift validation tests—often through Lambda hooks or target group health checks—to verify the application is functioning correctly. If these tests fail, CodeDeploy automatically triggers a rollback, replacing the new task set with the original one, which explains why the new task set is immediately replaced after a few minutes. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of CodeDeploy’s lifecycle hooks and the distinction between pre-traffic and post-traffic shift validations; a common trap is confusing a failing initial health check (which prevents traffic shift) with a failing post-traffic validation (which causes rollback). Memory tip: think “post-shift = rollback trigger”—if the app breaks after traffic moves, CodeDeploy pulls it back.
DVA-C02 Deployment Practice Question
This DVA-C02 practice question tests your understanding of deployment. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: codeDeploy blue/green deployments use post-traffic validation.. 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 developer is using AWS CodeDeploy to deploy an application to an Amazon ECS service with the Fargate launch type. The deployment uses a blue/green strategy. After the new task set is created and passes the initial health checks, the traffic is shifted to the new task set. However, the new task set is immediately replaced by the old one after a few minutes, causing a rollback. What is the most likely reason?
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.
Clue:
"immediately / without restart"Why it matters: Time or reboot constraint — the correct answer must take effect right away without requiring a reboot or reload.
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 new task set fails the post-traffic shift validation tests.
Option D is correct because in a blue/green deployment on ECS with CodeDeploy, after traffic is shifted to the new task set, CodeDeploy runs post-traffic shift validation tests (e.g., via Lambda hooks or target group health checks). If these tests fail, CodeDeploy automatically triggers a rollback by replacing the new task set with the original (old) task set. This matches the described behavior where the new task set is immediately replaced after a few minutes.
Key principle: CodeDeploy blue/green deployments use post-traffic validation.
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 lifecycle hooks for the new task set are failing.
Why it's wrong here
Lifecycle hooks run before traffic is shifted; if they fail, the deployment would not proceed to traffic shift, so this does not match the described sequence.
- ✗
The target group for the new task set is not configured correctly.
Why it's wrong here
Incorrect target group configuration might cause traffic routing issues, but it would not directly trigger a rollback; the deployment would likely complete with routing errors.
- ✗
The deployment group's rollback configuration triggers due to alarm threshold.
Why it's wrong here
Rollback due to CloudWatch alarms is possible, but the scenario states the rollback happens 'after a few minutes' immediately after traffic shift, which is typical of post-traffic validation failure, not an alarm that takes time to evaluate.
- ✓
The new task set fails the post-traffic shift validation tests.
Why this is correct
CodeDeploy performs validation after traffic shift; if the validation fails (e.g., health check failure or Lambda hook failure), it triggers an automatic rollback to the original task set.
Clue confirmation
The clue words "most likely", "immediately / without restart" in the question point toward this answer.
Related concept
CodeDeploy blue/green deployments use post-traffic validation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse pre-traffic shift hooks (which prevent traffic from being shifted) with post-traffic shift hooks (which cause a rollback after traffic is already shifted), leading them to incorrectly select lifecycle hook failures or target group misconfiguration.
Trap categories for this question
Scenario analysis trap
Rollback due to CloudWatch alarms is possible, but the scenario states the rollback happens 'after a few minutes' immediately after traffic shift, which is typical of post-traffic validation failure, not an alarm that takes time to evaluate.
Detailed technical explanation
How to think about this question
CodeDeploy's blue/green deployment for ECS uses a 'AfterAllowTraffic' hook to run post-traffic shift validation, such as a Lambda function that performs integration tests or checks application endpoints. If this hook returns a failure status (or times out), CodeDeploy considers the deployment unhealthy and initiates a rollback by redirecting traffic back to the original task set and terminating the new one. The default rollback behavior is to revert to the last successful deployment, which in this case is the old task set.
KKey Concepts to Remember
- CodeDeploy blue/green deployments use post-traffic validation.
- Post-traffic validation occurs after traffic is shifted to the new task set.
- Validation can include health checks or Lambda hooks (e.g., AfterAllowTraffic).
- Failure in post-traffic validation automatically triggers a rollback to the old task set.
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
CodeDeploy blue/green deployments use post-traffic validation.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. CodeDeploy blue/green deployments use post-traffic validation. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review codeDeploy blue/green deployments use post-traffic validation., then practise related DVA-C02 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Deployment — This question tests Deployment — CodeDeploy blue/green deployments use post-traffic validation..
What is the correct answer to this question?
The correct answer is: The new task set fails the post-traffic shift validation tests. — Option D is correct because in a blue/green deployment on ECS with CodeDeploy, after traffic is shifted to the new task set, CodeDeploy runs post-traffic shift validation tests (e.g., via Lambda hooks or target group health checks). If these tests fail, CodeDeploy automatically triggers a rollback by replacing the new task set with the original (old) task set. This matches the described behavior where the new task set is immediately replaced after a few minutes.
What should I do if I get this DVA-C02 question wrong?
Review codeDeploy blue/green deployments use post-traffic validation., then practise related DVA-C02 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "immediately / without restart". 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?
CodeDeploy blue/green deployments use post-traffic validation.
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Same concept, more angles
3 more ways this is tested on DVA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company uses AWS CodePipeline to deploy a containerized application to Amazon ECS with Fargate. The pipeline consists of a source stage (Amazon ECR), a build stage (CodeBuild), and a deploy stage (CodeDeploy with ECS Blue/Green). Recently, after a successful build, the deploy stage fails with the error 'Service deployment failed because the task definition is not compatible with the target group.' The task definition uses the 'awsvpc' network mode and specifies a port mapping of 80. The target group is configured to use port 80. What is the MOST likely cause of the failure?
hard- A.The task definition port mapping does not match the target group port.
- B.The task definition does not include a logging configuration for CloudWatch Logs.
- C.The task definition uses the 'awsvpc' network mode, which is not supported for Blue/Green deployments.
- ✓ D.The target group health check path is not configured correctly.
Why D: The error 'Service deployment failed because the task definition is not compatible with the target group' typically occurs when the target group's health check configuration is invalid or unreachable. In an ECS Blue/Green deployment with CodeDeploy, the target group health check path must be configured to return a valid HTTP response from the container; if the path is incorrect (e.g., missing or pointing to a non-existent endpoint), the target group marks instances as unhealthy, causing the deployment to fail even though the port mapping and network mode are correct.
Variation 2. A team is using AWS CodePipeline to deploy a critical application to Amazon ECS. The pipeline has a deployment stage that uses Amazon ECS (Blue/Green) action with CodeDeploy. Recently, the deployment failed because the new task set did not become healthy within the specified timeout. The team wants to ensure that future deployments automatically roll back if the health check fails. What should the team do?
hard- ✓ A.Create a CloudWatch alarm that triggers when the healthy task count of the ECS service falls below a threshold. Configure the CodeDeploy deployment group to automatically roll back when this alarm is in ALARM state.
- B.Modify the CodeDeploy deployment group to enable automatic rollback when a deployment fails. The deployment will automatically revert to the last successful deployment.
- C.Increase the deployment timeout in the CodeDeploy deployment configuration to allow more time for the new task set to become healthy.
- D.Configure the ECS service to automatically roll back to the previous task definition if the deployment fails. Use the ECS service's deployment circuit breaker.
Why A: Option A is correct because it leverages CloudWatch alarms to monitor the health of the ECS service's new task set. When the alarm triggers due to insufficient healthy tasks, CodeDeploy can automatically initiate a rollback to the previous revision. This approach provides a proactive, health-based rollback mechanism that directly addresses the failure condition described (new task set not becoming healthy within timeout).
Variation 3. A company deploys a critical application on Amazon ECS with Fargate using a blue/green deployment strategy with AWS CodeDeploy. The deployment group has two target groups, one for blue and one for green. The Application Load Balancer (ALB) is configured with a listener that forwards traffic to the blue target group initially. A recent deployment to the green environment failed, and the green service is in a steady state with zero healthy tasks. The developer needs to ensure that the blue service continues to serve traffic without interruption. The developer checks the CodeDeploy console and sees that the deployment is stuck in the 'InProgress' state with a status of 'Green fleet is not healthy.' What should the developer do to restore the deployment to a healthy state?
medium- A.Update the ECS task definition for the green service to a working version and wait for the deployment to complete.
- B.Manually update the ECS service for the blue environment to increase the desired count.
- ✓ C.Stop the deployment in CodeDeploy and re-point the ALB listener to the blue target group.
- D.Roll back the deployment to the previous version using the CodeDeploy console.
Why C: Option B is correct because stopping the deployment and rerouting traffic to the blue target group ensures the blue service continues to serve traffic. Option A is wrong because manually updating the blue service does not address the stuck deployment. Option C is wrong because updating the green service may not fix the deployment. Option D is wrong because rolling back may not be available if the deployment is stuck.
Last reviewed: Jun 11, 2026
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