Windows EC2 Downgrade from "g4dn.xlarge" to "g4ad.xlarge" for saving cost

Changing the instance type from "g4dn.xlarge" to "g4ad.xlarge" is not a straightforward downgrade, as these instance types have different underlying architectures and capabilities. The g4dn instances use NVIDIA GPUs, while g4ad instances use AMD GPUs. This difference in hardware architecture is likely the reason you're encountering issues with your launch configurations and templates.

To change the instance type in this case, you'll need to follow a migration process rather than a simple instance type change. Here's a general approach you can take:

1. First, create a backup of your current instance. This can be done by creating a snapshot or an AMI (Amazon Machine Image) of your existing instance.

2. Launch a new instance with the desired "g4ad.xlarge" type using a compatible AMI. Ensure that the AMI you choose supports the AMD GPU architecture.

3. Install and configure your application and any necessary drivers on the new instance. You may need to install AMD GPU drivers instead of NVIDIA drivers.

4. Migrate your data and configurations from the old instance to the new one.

5. If you're using an Elastic IP address, associate it with the new instance.

6. Test the new instance thoroughly to ensure everything is working as expected.

7. Update your Auto Scaling group to use the new instance type. You'll likely need to create a new launch template or launch configuration with the g4ad.xlarge instance type.

8. Once everything is working correctly with the new instance, you can terminate the old g4dn.xlarge instance.

The error you're encountering about AWS Marketplace product not being supported suggests that there might be licensing issues or incompatibilities with the current AMI when trying to use it with the g4ad instance type. You may need to select a different base AMI that's compatible with AMD GPUs and then reinstall your applications and configurations.

Remember to perform this migration during a maintenance window to minimize disruption to your services. Also, be aware that changing instance types may affect the performance and behavior of your applications, so thorough testing is crucial.

Sources
Migrate to a new instance type by launching a new EC2 instance - Amazon Elastic Compute Cloud
Migrate an EC2 Windows instance to the latest instance type | AWS re:Post