Final answer:
Amazon EC2 Auto Scaling is the AWS feature used to launch a pre-configured EC2 instance, automatically adjusting the number of instances based on demand.
Step-by-step explanation:
The AWS feature that can be used to launch a pre-configured Amazon Elastic Compute Cloud (EC2) instance is Amazon EC2 Auto Scaling. Amazon S3 is used for storage, Amazon RDS is for relational databases, and Amazon EC2 Container Service (now known as Amazon ECS) is for container management. Amazon EC2 Auto Scaling, on the other hand, allows you to automatically adjust the number of EC2 instances in response to changing demand, and it can also be used to launch a pre-configured EC2 instance based on specified criteria and configurations.