Starting today, customers can use Amazon EC2 On-Demand Capacity Reservations to reserve capacity for cluster placement groups. With cluster placement groups, customers can launch EC2 instances into logical groups within a segment of the network with high bisection bandwidth, thus getting low latency and high throughput between instances inside the cluster. Cluster placement groups are beneficial for customers with workloads that require tightly coupled node-to-node communication, such as high-performance computing (HPC) workloads or in-memory databases like SAP HANA. With the addition of On-Demand Capacity Reservations for cluster placement groups, customers can get the assurance of reserved capacity as they scale compute resources within their cluster.

Source: AWS