Cis K8S V1110 4.2.11

4.2.11 Verify that the RotateKubeletServerCertificate argument is set to true (Manual)

Profile Applicability

• Level 1 - Worker Node

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 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 take care of rotation yourself.

Impact

None

Audit

Ignore this check if serverTLSBootstrap is true in the kubelet config file or if the --rotate-server-certificates parameter is set on kubelet Run the following command on each node:

ps -ef | grep kubelet

Verify that RotateKubeletServerCertificate argument exists and is set to true.

Remediation

Edit the kubelet service file /etc/kubernetes/kubelet.conf on each worker node and set the below parameter in KUBELET_CERTIFICATE_ARGS variable.

--feature-gates=RotateKubeletServerCertificate=true

Based on your system, restart the kubelet service. For example:

systemctl daemon-reload
systemctl restart kubelet.service

Default Value

By default, kubelet server certificate rotation is enabled.

References

1. https://github.com/kubernetes/kubernetes/pull/45059
2. https://kubernetes.io/docs/admin/kubelet-tls-bootstrapping/#kubelet-configuration

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