If you want to deploy an Autoscaling EC2 infrastructure on AWS using ELB, you'll need to follow this steps:

1. Launch EC2 Instance
   • EC2 Dashboard > Launch Instance
   • Configure your web app
2. Transform into AMI
   • Select Instance > Action > Image > Create Image
   • Instance > Delete EC2 Instantes
   • Delete Security Group created with the Instance
3. Deploy AMI across different zones
   • Load Balancer > Create Load Balancer > Application Load Balancer
   • Select Zones
4. Configure Secure Groups
   • Create New Secure Group
5. Configure Target Groups
   • Define a Target Group name
6. Launch Configurations
   • Choose the AMI created early
   • Define Launch Configuration name
   • Allow traffic just to the Load Balancer Security Group
7. Configure the Autoscaling Group
   • Autoscaling Group > Create Autoscaling Group
   • Define Name
   • Group Size
   • Choose the subnets
   • Choose Target Groups
   • Health Check Type: ELB
8. Define the Scaling Policies
   • Create Increase and Decrease Alarms
   • Set Notifications

The Autoscaling Group will launch the AMI instances based on the Increase/Decrease alarms and the minimal requirements.

References

Elastic Load Balancing - https://aws.amazon.com/elasticloadbalancing/
Elastic Compute Cloud - https://aws.amazon.com/ec2/