The correct way to measure tcp performance between ec2 instances

Question

I used qperf tool to measure the latency between AWS EC2 instances. First I tested tcp latency between two c5xlarge instances and I got latency of 30 micro seconds. Later I terminated those instance and try the test in new two c5xlarge instances. There I got latency of 65 micro seconds. What could be reason for this deviation of results?

Note: There were some other instances in the VPC I created my test instances.

What would be the correct methodology to conduct this kind of test?

Answer 1

The number of instances in a VPC would not impact this metric. All networking is virtual. First, make sure the instances are in the same Availability Zone.

Then, you could try using a Placement Group with the Cluster option:

Packs instances close together inside an Availability Zone. This strategy enables workloads to achieve the low-latency network performance necessary for tightly-coupled node-to-node communication that is typical of HPC applications.