A DevOps engineer maintains a web application that is deployed on an Amazon Elastic Container...

The key requirement is to shift a small percentage of traffic to a new version first to validate changes before rolling out to the entire ECS service, thereby reducing downtime and deployment risk. For ECS services behind an Application Load Balancer, the AWS-recommended and most reliable approach is to use AWS CodeDeploy with blue/green or canary deployments.

Option B directly addresses this requirement. By configuring the ECS service to use CodeDeploy as the deployment controller, CodeDeploy can manage traffic shifting between two ALB target groups: one for the current (stable) version and one for the new version. The CodeDeployDefault.ECSCanary10Percent15Minutes deployment configuration initially routes 10% of production traffic to the new task set, monitors the deployment for issues, and then shifts the remaining traffic after the defined interval. This enables early detection of application errors while limiting user impact.

Option A and C rely on rolling updates, which replace tasks incrementally but do not provide precise traffic control or automated rollback based on health checks. Option D’s slow start setting only affects how quickly targets receive traffic after registration and does not implement true canary testing.

Therefore, using AWS CodeDeploy with ECS canary deployments is the most robust, AWS-supported solution to test changes safely before full rollout.