Which service can automatically scale resources in response to demand?

Amazon EC2 Auto Scaling is designed specifically to automatically adjust the number of Amazon EC2 instances in response to changes in demand. This service monitors the specified metrics and conditions, such as CPU utilization or memory usage, and dynamically scales the number of instances up or down based on these metrics. This capability ensures that applications have the necessary resources during peak demand periods while minimizing costs during low usage times.

Choosing Amazon EC2 Auto Scaling enables businesses to maintain performance and availability without manual intervention, providing an efficient way to manage resource allocation. Its functionality to set policies for scaling actions also integrates well with other AWS services, allowing for more complex architectures where resource optimization is critical.

In contrast, while AWS Lambda also scales automatically, it does so in a different context, operating on a serverless model where individual functions execute in response to events without the need for direct server management. Amazon RDS offers managed relational database services, and while it can handle scaling to an extent through read replicas and instance resizing, it doesn't automatically scale in the same adaptive manner as EC2 Auto Scaling when it comes to varying server workloads. Lastly, Amazon EFS provides scalable file storage and can increase storage capacity automatically, but it doesn't scale compute resources directly in response to demand like EC2 Auto