If your compute layer needs the lowest possible latency and the highest possibly packet per second network performance consider using cluster placement groups.
A cluster placement group is a logical grouping of instances within a single Availability Zone. A cluster placement group can span peered VPCs in the same Region. Instances in the same cluster placement group enjoy a higher per-flow throughput limit of up to 10 Gbps for TCP/IP traffic and are placed in the same high-bisection bandwidth segment of the network.
AWS recommend that you launch your instances in the following way:
Use a single launch request to launch the number of instances that you need in the placement group.
Use the same instance type for all instances in the placement group.