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aws-auth-controller

Managing the aws-auth ConfigMap

Problem

Access to the Kubernetes-API of an EKS cluster is managed through IAM roles that are mapped to RBAC users and groups. This mapping is stored in a configmap named aws-auth in the kube-system namespace.

This configmap is created by EKS as soon as the first nodegroup is created so that the nodes themselves can access the API. To grant access for other users, this configmap needs to be edited. The details are found in the EKS documentation.

This editing procedure is a bit complex to automate in CI. Due to the centralized nature of the configmap it is also difficult to add and remove entries in a distruibuted manner, depending on your deployment strategy.

The solution

The controller takes care of editing the aws-auth configmap. It takes snippets of it as input and makes sure the configmap stays in sync with the desired access configuration.

Usage

The snippets are defined in custom resources that can be placed in any namespace throughout the cluster. They follow the same semantics as the aws-auth configmap itself.

To pick up on the example from the AWS documentation, that snippet would look like this in the CR:

apiVersion: crd.awsauth.io/v1beta1
kind: AwsAuthMapSnippet
metadata:
  name: awsauthmapsnippet-sample
  namespace: sample-namespace
spec:
  mapRoles:
    - rolearn: arn:aws:iam::111122223333:role/eksctl-my-cluster-nodegroup-standard-wo-NodeInstanceRole-1WP3NUE3O6UCF
      username: system:node:{{EC2PrivateDNSName}}
      groups:
        - system:bootstrappers
        - system:nodes
  mapUsers:
    - userarn: arn:aws:iam::111122223333:user/admin
      username: admin
      groups:
        - system:masters
    - userarn: arn:aws:iam::111122223333:user/ops-user
      username: ops-user
      groups:
        - system:masters

When this resource is added to the cluster, the controller will modify the configmap to include the entries in this snippet. When it is removed, the respective entries will be removed, too.

Controller deployment

A working single-file deployment manifest is forthcoming. For now the manifests under configs can be used as a guide.

The CRD is best created this way:

make manifests
kubectl kustomize config/crd > crd.yaml

Development

This project was created with kubebuilder 3.1.8 using go 1.16. See the documentation for more information.

To try out the controller locally against a running cluster, simply do

make install # apply crd to cluster
make run ENABLE_WEBHOOKS=false

It will use whatever kubectl context is currently active.

TODOs

  • A validating webhook to check with AWS if ARN actually exists (?, needs IRSA)
  • Add mapAccounts if anybody needs it
  • More tests