Amazon's EKS is still in preview. I wouldn't expect it to be generally available (that is, stable) for several months at least. I've also heard reports that getting into the preview is really difficult at the moment.
> Alpha This is an experimental release as part of the Amazon EKS Preview. Interfaces and functionality may change. Expect bugs (and please help us squash them). DO NOT use for production workloads.
It's using a new networking model: https://github.com/aws/amazon-vpc-cni-k8s
> Alpha This is an experimental release as part of the Amazon EKS Preview. Interfaces and functionality may change. Expect bugs (and please help us squash them). DO NOT use for production workloads.