Cis Eks V160 3.2.9

3.2.9 Ensure that the RotateKubeletServerCertificate argument is set to true (Automated)

Profile Applicability

• Level 1

Description

Enable kubelet server certificate rotation.

Rationale

RotateKubeletServerCertificate causes the kubelet to both request a serving certificate after bootstrapping its client credentials and rotate the certificate as its existing credentials expire. This automated periodic rotation ensures that the there are no downtimes due to expired certificates and thus addressing availability in the CIA (Confidentiality, Integrity, and Availability) security triad.

Note: This recommendation only applies if you let kubelets get their certificates from the API server. In case your kubelet certificates come from an outside authority/tool (e.g. Vault) then you need to implement rotation yourself.

Audit Procedure

Audit Method 1:

First, SSH to each node. Run the following command to find the Kubelet process:

ps -ef | grep kubelet

If the output of the command above includes the --rotate-kubelet-server-certificate executable argument verify that it is set to true.

If the process does not have the --rotate-kubelet-server-certificate executable argument then check the Kubelet config file. The output of the above command should return something similar to --config /etc/kubernetes/kubelet/kubelet-config.json which is the location of the Kubelet config file.

Open the Kubelet config file:

cat /etc/kubernetes/kubelet/kubelet-config.json

Verify that the RotateKubeletServerCertificate argument is set to true.

Remediation

Remediation Method 1:

If modifying the Kubelet config file, edit the kubelet-config.json file /etc/kubernetes/kubelet/kubelet-config.json and set the below parameter to true:

"RotateKubeletServerCertificate":true

Additionally, ensure that the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubelet-args.conf does not set the --RotateKubeletServerCertificate executable argument to false because this would override the Kubelet config file.

Remediation Method 2:

If using executable arguments, edit the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubelet-args.conf on each worker node and add the below parameter at the end of the KUBELET_ARGS variable string.

--RotateKubeletServerCertificate=true

Default Value

See the Amazon EKS documentation for the default value.

References

1. https://github.com/kubernetes/kubernetes/pull/41912
2. https://kubernetes.io/docs/reference/command-line-tools-reference/kubelet-tls-bootstrapping/#kubelet-configuration
3. https://kubernetes.io/docs/imported/release/notes/
4. https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates/
5. https://kubernetes.io/docs/tasks/administer-cluster/reconfigure-kubelet/

CIS Controls