According to the official kubernetes documentation, in order for your nodes to get access to AWS ECR, the following flag needs to be added to ~/.kube/config:

iam:
  allowContainerRegistry: true
  legacy: false

Then, after updating the cluster, the following permissions should be added to your ec2 instances:

{
  "Sid": "kopsK8sECR",
  "Effect": "Allow",
  "Action": [
    "ecr:BatchCheckLayerAvailability",
    "ecr:BatchGetImage",
    "ecr:DescribeRepositories",
    "ecr:GetAuthorizationToken",
    "ecr:GetDownloadUrlForLayer",
    "ecr:GetRepositoryPolicy",
    "ecr:ListImages"
  ],
  "Resource": [
    "*"
  ]
}

However, I just created a cluster on AWS using kops and my nodes already have those permissions, without me doing any additional config stuff.

Is this normal?

$ kops version
Version 1.8.0 (git-5099bc5)

$ kubectl version    
Client Version: version.Info{Major:"1", Minor:"8", GitVersion:"v1.8.1", GitCommit:"f38e43b221d08850172a9a4ea785a86a3ffa3b3a", GitTreeState:"clean", BuildDate:"2017-10-11T23:27:35Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"8", GitVersion:"v1.8.4", GitCommit:"9befc2b8928a9426501d3bf62f72849d5cbcd5a3", GitTreeState:"clean", BuildDate:"2017-11-20T05:17:43Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}