Classification:

compliance

Framework:

cis-kubernetes

Control:

4.2.12

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Set up the kubernetes integration.

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.

Audit

Run the following command on each node: ps -ef | grep kubelet. Verify that RotateKubeletServerCertificate argument exists and is set to true.

Remediation

On the master edit /var/lib/kubelet/kubeadm-flags.env and set the parameter KUBELET_CERTIFICATE_ARGS --feature-gates=RotateKubeletServerCertificate=true or as an alternative, and suggested as a last resort, edit the kubelet service file /etc/systemd/system/kubelet.service.d/10-kubeadm.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

Impact

None

Default value

By default, kubelet server certificate rotation is disabled.

References

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

CIS controls

Version 6.14.2 Encrypt All Sensitive Information Over Less-trusted Networks - All communication of sensitive information over less-trusted networks should be encrypted. Whenever information flows over a network with a lower trust level, the information should be encrypted.

Version 7.14.4 Encrypt All Sensitive Information in Transit - Encrypt all sensitive information in transit.