You can now create Amazon EC2 On-Demand Capacity Reservations through AWS CloudFormation. You can make Capacity Reservations part of the provisioning strategy as you set up your cloud environments. Take advantage of On-Demand Capacity Reservations if you have specific requirements around instance type, instance size, instance capability, and Availability Zones, and if you need higher levels of assurance that you will be able to launch (or relaunch) into a specific capacity.
On-Demand Capacity Reservations let you reserve Amazon EC2 capacity for any duration. You can reserve the exact capacity you need, in the location you need, and can keep it only for as long as you need it. On-Demand Capacity Reservations are activated as soon as they are requested, and they stay active until cancelled. Once created, the EC2 capacity is held for you regardless of whether you run the instances or not. If you have Regional RI discounts, they will automatically apply to any matching Capacity Reservation. This gives you the flexibility to selectively add capacity reservations and still get the Regional RI discounts for that usage.
On-Demand Capacity Reservations are available in all public Regions. Visit AWS CloudFormation user guide to learn more about adding Capacity Reservations to your CloudFormation template. To learn more about Capacity Reservations and how to use them, visit FAQs, Linux or Windows user guides. You can also create and manage Capacity Reservations through the AWS Management Console, AWS SDK and CLI.
from What’s New https://aws.amazon.com/about-aws/whats-new/2019/04/now-create-amazon-ec2-on-demand-capacity-reservations-through-aws-cloudformation/