EKS cluster doesn't provide client-ca-file

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Created a cluster in EKS (Kubernetes 1.11.5) with multiple node groups however I'm noticing that in the extension-apiserver-authentication configmap that client-ca-file key is missing.

I assume this is due to the way Kubernetes API service is initiated. Has anyone else come across this issue ?

I came across this problem while deploying certificate manager which queries the api server with GET https://10.100.0.1:443/api/v1/namespaces/kube-system/configmaps/extension-apiserver-authentication.

In GKE this isnt a problem as extension-apiserver-authentication configmap already includes client-ca-file.

extension-apiserver-authentication configmap in AWS,

apiVersion: v1
data:
  requestheader-allowed-names: '["front-proxy-client"]'
  requestheader-client-ca-file: |
    <certificate file>
  requestheader-extra-headers-prefix: '["X-Remote-Extra-"]'
  requestheader-group-headers: '["X-Remote-Group"]'
  requestheader-username-headers: '["X-Remote-User"]'
kind: ConfigMap
metadata:
  creationTimestamp: 2019-01-14T04:56:51Z
  name: extension-apiserver-authentication
  namespace: kube-system
  resourceVersion: "39"
  selfLink: /api/v1/namespaces/kube-system/configmaps/extension-apiserver-authentication
  uid: ce2b6f64-17b8-11e9-a6dd-021a269d3ce8

However in GKE,

apiVersion: v1
data:
  client-ca-file: |
    <client certificate file>
  requestheader-allowed-names: '["aggregator"]'
  requestheader-client-ca-file: |
    <certificate file>
  requestheader-extra-headers-prefix: '["X-Remote-Extra-"]'
  requestheader-group-headers: '["X-Remote-Group"]'
  requestheader-username-headers: '["X-Remote-User"]'
kind: ConfigMap
metadata:
  creationTimestamp: 2018-05-24T12:06:33Z
  name: extension-apiserver-authentication
  namespace: kube-system
  resourceVersion: "32"
  selfLink: /api/v1/namespaces/kube-system/configmaps/extension-apiserver-authentication
  uid: e6c0c431-5f4a-11e8-8d8c-42010a9a0191
amazon-eks kubernetes authentication
2 Answers

I've also run into this issue while trying to use cert-manager on an AWS EKS cluster. It is possible to inject the certificate yourself using the certificate obtained from the AWS CLI. Follow these steps to address this issue:

Obtain the Certificate

The certificate is stored Base64 encoded and can be retrieved using

aws eks describe-cluster \
        --region=${AWS_DEFAULT_REGION} \
        --name=${CLUSTER_NAME} \
        --output=text \
        --query 'cluster.{certificateAuthorityData: certificateAuthority.data}' | base64 -D

Inject the Certificate

Edit configMap/extension-apiserver-authentication under the kube-system namespace: kubectl -n kube-system edit cm extension-apiserver-authentication

Under the data section, add the CA under a new config entry named client-ca-file. For example:

  client-ca-file: |
    -----BEGIN CERTIFICATE-----
...
    -----END CERTIFICATE-----
user_7941780

Your assumptions might be correct, I mean your issue might really have to do with the way how api-server is initiated in EKS, and when lacking the --client-ca-file option, according the apiserver source code:

Cluster doesn't provide client-ca-file in configmap/%s in %s, so client certificate authentication to extension api-server won't work.

I`m wondering if you could create a client-ca by yourself, and update afterwards extension-apiserver-authentication ConfigMap. After all in EKS we have access to CA (the way to get it here), which can serve us to sign the client certificates, like described in GitHub page with sample api-server.

As a side comment:

I noticed, that on EKS, components like kubelet , are using aws-iam-authenticator (content of /var/lib/kubelet/kubeconfig on cluster node):

apiVersion: v1
kind: Config
users:
- name: kubelet
  user:
    exec:
      apiVersion: client.authentication.k8s.io/v1alpha1
      args:
      - token
      - -i
      - eks-api-eval
      command: /usr/bin/aws-iam-authenticator
      env: null

in opposite to GKE, where client-ca is used as a way for authenticating clients:

apiVersion: v1
kind: Config
users:
- name: kubelet
  user:
    client-certificate: /etc/srv/kubernetes/pki/kubelet.crt
    client-key: /etc/srv/kubernetes/pki/kubelet.key
user_103477940
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