K
Q

CIS benchmark issue for Kubernetes cluster

4/3/2021

I'm running the CIS kube-bench tool on the master node and trying to resolve this error 

[FAIL] 1.2.6 Ensure that the --kubelet-certificate-authority argument is set as appropriate (Automated).

I understand that I need to update the API server manifest YAML file with this flag pointing to the right CA file --kubelet-certificate-authority however, I'm not sure which one is the right CA Certififace for Kubelet.

These are my files in the PKI directory:-

apiserver-etcd-client.crt
apiserver-etcd-client.key
apiserver-kubelet-client.crt
apiserver-kubelet-client.key
apiserver.crt
apiserver.key
ca.crt
ca.key
etcd
front-proxy-ca.crt
front-proxy-ca.key
front-proxy-client.crt
front-proxy-client.key
sa.key
sa.pub
-- vinod827
kubernetes
security

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2 Answers

4/3/2021

By default in Kubernetes there are 3 different Parent CA (kubernetes-ca, etcd-ca, kubernetes-front-proxy-ca). You are looking for kubernetes-ca because kubelet using kubernetes-ca, and you can check the documentation. kubernetes-ca default path is /etc/kubernetes/pki/ca.crt But also you verify it via kubelet configmap with below commands

kubectl get configmap -n kube-system $(kubectl get configmaps -n kube-system | grep kubelet  | awk '{print $1}') -o yaml | grep -i clientca
-- Kağan Mersin
Source: StackOverflow
4/3/2021

3 very similar discussions on the same topic. I wont provide you all steps cause it well written in documentation and related questions on stack. Only high-level overview

  1. How Do I Properly Set --kubelet-certificate-authority apiserver parameter?
  2. Kubernetes kubelet-certificate-authority on premise with kubespray causes certificate validation error for master node
  3. Kubernetes kubelet-certificate-authority on premise with kubespray causes certificate validation error for master node

Your actions:

These connections terminate at the kubelet's HTTPS endpoint. By default, the apiserver does not verify the kubelet's serving certificate, which makes the connection subject to man-in-the-middle attacks and unsafe to run over untrusted and/or public networks.

Then, edit the API server pod specification file /etc/kubernetes/manifests/kube-apiserver.yaml on the master node and set the --kubelet-certificate-authority parameter to the path to the cert file for the certificate authority.

From @Matt answer

  • Use /etc/kubernetes/ssl/ca.crt to sign new certificate for kubelet with valid IP SANs.
  • Set --kubelet-certificate-authority=/etc/kubernetes/ssl/ca.crt (valid CA).
  • In /var/lib/kubelet/config.yaml (kubelet config file) set tlsCertFile and tlsPrivateKeyFile to point to newly created kubelet crt and key files.

And from clarifications:

Yes you have to generate certificates for kubelets and sign sign them the provided certificate authority located here on the master /etc/kubernetes/ssl/ca.crt

-- Vit
Source: StackOverflow