Auto Scaling:Overview

Choose an instance configuration source

Use a scaling configuration when:

• Your scaling group serves ECS instances or elastic container instances (ECI).

• You need parameter validation at creation time — a scaling configuration won't save if required parameters like the image are missing, which eliminates a whole class of scale-out failures.

• You need Pay-as-you-go or Spot Instance billing.

• You want to select up to 20 instance types to increase the success rate of scale-outs.

Use a Launch Template when:

• Your scaling group is ECS type only.

• You already maintain launch templates in the ECS console and want to reuse them directly.

• You need Subscription billing.

• You need to manage multiple versioned configurations — launch templates support creating new versions without modifying the original. For example, you can create a base template without an image, then create a new version that adds the image and user data for a specific application release.

The following table summarizes the key differences.

Set an instance configuration source

There are three ways to set the instance configuration source for a scaling group.

Select Existing Instance

When you create a scaling group, set Instance Configuration Source to Select Existing Instance. Auto Scaling automatically creates a scaling configuration from the selected instance's parameters and enables the scaling group.

No new image is created. The scaling configuration uses the image ID from the original instance. If that image ID no longer exists, scale-outs will fail.

Launch Template

When you create a scaling group, set Instance Configuration Source to Launch Template and select an existing template. The scaling group is automatically enabled.

Create a scaling configuration

Create the scaling group first (set Instance Configuration Source to Create from Scratch — the group enters a Disabled state), then create a scaling configuration and apply it to the group. This approach gives you the most control over instance parameters.

Compare parameters

The parameters available differ across the three source types. The following tables show which parameters each source supports, organized by category.

Manage instance configuration sources