This is actually pretty well described in the docs.

> Before you create worker nodes, you must create an IAM role with the
> following IAM policies:
> 
> AmazonEKSWorkerNodePolicy
> 
> AmazonEKS_CNI_Policy
> 
> AmazonEC2ContainerRegistryReadOnly


Also you need to make sure that this role could be assumed by EKS.

    {
      "Version": "2012-10-17",
      "Statement": [
        {
          "Effect": "Allow",
          "Principal": {
            "Service": "ec2.amazonaws.com"
          },
          "Action": "sts:AssumeRole"
        }
      ]
    }