It is actually based on the ec2 instance type you decide to boot, and generally the bigger the instance the more ENI's you can attach. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-en...

The EC2 k8s network driver they wrote essentially will attach/detach extra ENI's on the fly and pre-allocate IP addresses to your EC2 host to allow for fast pod spin up/down.

I found this article pretty helpful to explain some of the AWS differences: https://www.contino.io/insights/kubernetes-is-hard-why-eks-m...