The correct choice is: Use AWS Application Auto Scaling with target tracking policies that automatically adjust the ECS service count when CPU or memory utilization crosses a defined threshold in CloudWatch.

When using Amazon ECS with the Fargate launch type, you dont manage the underlying EC2 instances directly. Instead, ECS services scale by increasing or decreasing the number of running tasks. AWS Application Auto Scaling supports ECS and provides target tracking policies that automatically adjust task counts based on metrics like CPU or memory utilization. This approach offers dynamic responsiveness to workload changes and eliminates the need for manual intervention or predictive scheduling.

The option Deploy an AWS Lambda function that responds to CloudWatch alarms by scaling the number of ECS tasks up or down manually adds unnecessary operational overhead. While technically possible, using Lambda for scaling is not ideal when built-in scaling mechanisms like Application Auto Scaling already exist for ECS services and offer native support with less complexity.

The option Schedule Amazon EC2 Auto Scaling actions to adjust resource capacity based on historical usage patterns and expected traffic windows may sound viable but is not applicable to Fargate, which does not use EC2 instances directly. Also, scheduled scaling alone lacks the flexibility to respond to unexpected demand changes in real time.

The option Configure Amazon EC2 Auto Scaling with basic scaling rules to respond to ECS service metrics from CloudWatch alarms is also incorrect, as EC2 Auto Scaling is meant for EC2-based infrastructure. It is not compatible with Fargate, which abstracts away the server management layer entirely.

This question is important because it tests your ability to distinguish between EC2-based scaling strategies and the serverless model offered by Fargate. The key to choosing the right answer lies in recognizing that Fargate tasks scale at the service level, and that Application Auto Scaling is the native service that controls this behavior.

One tip for questions like this: always look for the most native, managed, and scalable solution. If youre working with ECS Fargate, Application Auto Scaling is the intended mechanismnot EC2 tools or custom Lambda logic. This question is tricky because it includes realistic-sounding but incompatible solutions that apply only to EC2-backed clusters, not to Fargates serverless architecture.

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