AWS EC2 Change Instance Type Advanced details CPU options Specify CPU options pricing

When changing your EC2 instance type from r6a.12xlarge to r6a.24xlarge and using the "Specify CPU options" feature under Advanced details, there are no additional or hidden costs associated with customizing the CPU options. The pricing remains based on the On-Demand Linux pricing per hour for the selected instance type.

Specifying CPU options, such as the number of cores or threads per core, does not incur any extra charges. You will be billed the same amount as you would for instances launched with default CPU options. In your case, the cost would indeed change from 1.7160 USD per hour to 3.4320 USD per hour, as you mentioned, solely due to the instance type change.

The ability to specify CPU options is primarily designed to help optimize performance for specific workloads or to potentially reduce software licensing costs that are based on the number of CPUs or cores. For example, if you have software licensed per CPU, you might choose to use fewer cores to reduce those licensing costs. However, this is separate from AWS pricing and depends on your specific software licensing agreements.

It's important to note that while customizing CPU options can help with optimization, it doesn't affect the base cost of the EC2 instance itself. The pricing remains tied to the instance type (in this case, r6a.24xlarge), regardless of how you configure the CPU options.

In summary, you can adjust the CPU options without worrying about additional AWS charges. The cost will be based on the standard On-Demand Linux pricing for the r6a.24xlarge instance type, which is 3.4320 USD per hour as you correctly stated.
Sources
CPU options for Amazon EC2 instances - Amazon Elastic Compute Cloud
Retaining Optimize CPUs configuration during Amazon EC2 scaling to save on licensing costs | AWS Compute Blog
ModifyInstanceCpuOptions - Amazon Elastic Compute Cloud