AWS Auto Scaling monitors your applications and automatically adjusts capacity to maintain steady, predictable performance at the lowest possible cost. It is designed to be used with a variety of AWS services to enable a scalable and cost-optimized architecture. In contrast, AWS Lambda is a serverless compute service that runs your code in response to events and automatically manages the underlying compute resources, but it does not offer traditional scaling of resources. Amazon CloudWatch monitors your AWS resources and applications, providing metrics and alarms but does not directly adjust resources. Amazon EC2 instances are virtual servers in the cloud, and while they can be part of an Auto Scaling group, they themselves do not auto-scale.