Allocation strategies for multiple instance types - Amazon EC2 Auto Scaling
On-Demand Instances
This documentation is a draft for private preview for regions in the AWS European Sovereign Cloud. Documentation content will continue to evolve. Published: December 30, 2025.

Allocation strategies for multiple instance types

When you use multiple instance types, you manage how Amazon EC2 Auto Scaling fulfills your from the possible instance types. To do this, you specify .

To review the best practices for a mixed instances group, see Setup overview for creating a mixed instances group.

On-Demand Instances

Amazon EC2 Auto Scaling provides the following allocation strategies that can be used for On-Demand Instances:

prioritized

When fulfilling On-Demand capacity, Amazon EC2 Auto Scaling determines which instance type to use first based on the order of instance types in the list of launch template overrides. For example, let's say that you specify three launch template overrides in the following order: c5.large, c4.large, and c3.large. When your On-Demand Instances launch, the Auto Scaling group fulfills On-Demand capacity in the following order: c5.large, c4.large, and then c3.large.

Consider the following when managing the priority order of your On-Demand Instances:

  • You can pay for usage upfront to get significant discounts for On-Demand Instances by using Savings Plans or Reserved Instances. For more information, see the Amazon EC2 pricing page.

  • With Reserved Instances, your discounted rate of the regular On-Demand Instance pricing applies if Amazon EC2 Auto Scaling launches matching instance types. Therefore, if you have unused Reserved Instances for c4.large, you can set the instance type priority to give the highest priority for your Reserved Instances to a c4.large instance type. When a c4.large instance launches, you receive the Reserved Instance pricing.