Amazon EC2 Auto Scaling
User Guide

Using a Load Balancer With an Auto Scaling Group

You can automatically increase the size of your Auto Scaling group when demand goes up and decrease it when demand goes down. As the Auto Scaling group adds and removes Amazon EC2 instances, you must make sure that the traffic for your application is distributed across all of your instances. The Elastic Load Balancing service automatically routes incoming web traffic across such a dynamically changing number of instances. Your load balancer acts as a single point of contact for all incoming traffic to the instances in your Auto Scaling group. For more information, see the Elastic Load Balancing User Guide.

To use a load balancer with your Auto Scaling group, create the load balancer and then attach it to the group.