This documentation is a draft for private preview for regions in the AWS European Sovereign Cloud. Documentation content will continue to evolve. Published: December 31, 2025.

Setup overview for creating a mixed instances group

This topic provides an overview and best practices for creating an Auto Scaling mixed instances group.

Instance type flexibility

To enhance availability, deploy your application across multiple instance types. It's a best practice to use multiple instance types to satisfy capacity requirements. This way, Amazon EC2 Auto Scaling can launch another instance type if there is insufficient instance capacity in your chosen Availability Zones.

We recommend being flexible across at least 10 instance types for each workload.

Availability Zone flexibility

We strongly recommend that you span your Auto Scaling group across multiple Availability Zones. With multiple Availability Zones, you can design applications that automatically fail over between zones for greater resiliency.

As an added benefit, you can access a deeper Amazon EC2 capacity pool when compared to groups in a single Availability Zone. Because capacity fluctuates independently for each instance type in each Availability Zone, you can often get more compute capacity with flexibility for both the instance type and the Availability Zone.

For more information about using multiple Availability Zones, see Example: Distribute instances across Availability Zones.

Regional availability of instance types

The availability of EC2 instance types varies depending on your AWS Region. For example, the newest generation instance types might not yet be available in a given Region. Due to the variances in instance availability across Regions, you might encounter issues when making programmatic requests if multiple instance types in your overrides are not available in your Region. Using multiple instance types that are not available in your Region might cause the request to fail entirely. To solve the issue, retry the request with different instance types, making sure that each instance type is available in the Region. To search for instance types offered by location, use the describe-instance-type-offerings command. For more information, see Finding an Amazon EC2 instance type in the Amazon EC2 User Guide.

Limitations

After you add overrides to an Auto Scaling group using a mixed instances policy, you can update the overrides with the UpdateAutoScalingGroup API call but not delete them. To completely remove the overrides, you must first switch the Auto Scaling group to use a launch template or launch configuration instead of a mixed instances policy. Then, you can add a mixed instances policy again without any overrides.