AWS Network Adapters ENI and ENA

Hello Sam,

1) Let us say we have a VPC that has two subnets and each subnet has 10 EC2 machines. Do you normally configure one ENI for each EC2 machine (10) or one for each subnet (2) or one for the VPC (1)?

An Elastic Network Interface, or ENI, can be thought of as a virtual network card for your VM. You need at least one ENI (Primary ENI) per EC2, to be able to communicate with it (you can attach more than one ENI to an instance if you need to). A single ENI therefore cannot be shared between EC2 machines. Also there is no way to attach them to subnets or vpc.

Elastic network interfaces https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#eni-basics

2) ENI supports up to 10 GBPS. Does this mean if network or transit gateway supports a bandwidth of 50 GBPS the actual traffic will flow at max of 10 GBPS due to ENI restriction?

The following document explains how EC2 bandwidth specifications apply.

Amazon EC2 instance network bandwidth https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-network-bandwidth.html

Transit Gateway supports Up to 100 Gbps Bandwidth per VPC attachment per Availability Zone. The Transit Gateway bandwidth will be shared between all resources in a VPC in a single Availability Zone. However bandwidth limit per EC2 instance still applies.

Consider this similar to a personal laptop which supports 5 Gbps transfer speeds. Buying a 10 Gbps Internet connection is not going to increase the transfer speed of the laptop.

3) For network slow performance problems, shall we always try to upgrade from ENI to ENA?

Enhanced networking is definitely one way to improve network performance. There are several other factors in play when it comes to slow network performance. You may find this article helpful: https://repost.aws/knowledge-center/network-issue-vpc-onprem-ig