You can use the cluster placement groups to group instances together in a configuration to allow for very low network latency. Cluster placement groups allow for the non-blocking, non-oversubscribed, fully bi-sectional nature of the connectivity, meaning that instances in a placement group will be able to utilize the full line rate of 10 GBps to talk to each other. To place instances in a cluster placement group, we need to start the instances at the same time.