Which AWS feature automatically adjusts the number of Amazon EC2 instances in use based on current application load?

Auto Scaling groups automatically adjust the number of Amazon EC2 instances in use to maintain application availability and allow you to scale your EC2 capacity up or down automatically according to conditions you define. This ensures your application can handle varying loads efficiently. Dedicated Hosts provide physical EC2 servers for your exclusive use, offering licensing flexibility but not automatic scaling. Placement groups influence the placement of instances for performance or high availability, but they don't automatically scale the number of instances. Reserved Instances are a billing discount for committing to a specific instance configuration for a 1- or 3-year term, not a scaling mechanism.