Overview

An Auto Scaling Group (ASG) is a crucial AWS feature that automatically adjusts the number of EC2 instances in response to traffic fluctuations. This ensures optimal performance while minimizing costs.

Key Features of ASG

1. Scaling Mechanisms

• Scale Out (Increase Instances) → Adds EC2 instances when load increases.
• Scale In (Decrease Instances) → Removes EC2 instances when load decreases.
• The ASG dynamically adjusts its size based on demand.

2. Capacity Settings

ASG configurations include three capacity parameters:

• Minimum Capacity → The lowest number of EC2 instances (e.g., 2).
• Desired Capacity → The target number of EC2 instances (e.g., 4).
• Maximum Capacity → The highest number of EC2 instances (e.g., 7).

3. Health Management & Integration with Load Balancer

• If an EC2 instance becomes unhealthy, ASG terminates and replaces it automatically.
• ASG works with an Elastic Load Balancer (ELB) to distribute traffic evenly across healthy instances.
• The ELB performs health checks and informs the ASG, ensuring only healthy instances serve traffic.

4. Launch Templates

To create an ASG, you need a Launch Template (replacing the now-deprecated Launch Configuration). A launch template includes:

• AMI (Amazon Machine Image)
• Instance type