You can now use Amazon EC2 On-Demand Capacity Reservations (ODCRs) while creating clusters in Amazon EMR. When rotating a long running cluster, you might have strict requirements on the instance types and Availability Zones for the new instances you provision. Using Capacity Reservations, you can get capacity assurance to complete the cluster rotation without interruptions. You can also use Capacity Reservations to provision a group of successive short-lived clusters for individual workloads such that when you terminate a cluster, the next cluster can use the Capacity Reservations.
Source:: Amazon AWS