Amazon EC2 Auto Scaling is designed to automatically adjust the number of Amazon EC2 instances in response to the changing demand for an application, to ensure consistent performance and to minimize costs. It is the correct service for adding or removing EC2 instances automatically. AWS Lambda is a serverless compute service that runs code in response to events but does not deal with EC2 instances directly. Amazon S3 is a storage service and does not provide compute scaling capabilities. AWS CloudFormation is an infrastructure as code service that allows you to model and provision AWS resources but does not automatically scale EC2 instances according to demand.