docs/doc/source/security/kubernetes/kubernetes-root-ca-certificate.rst

Install Custom Kubernetes Root CA Certificate

By default, the K8S Root certificate and key are auto-generated and result in the other Kubernetes certificates being signed by an internal not well-known ; for example, for the Kubernetes API server certificate.

It is optional that you update the Kubernetes Root with a custom Root certificate and key, generated by yourself, and trusted by external servers connecting to the ’s Kubernetes API endpoint

The installation of the custom Kubernetes Root certificate can only be done during system deployment by using bootstrap overrides.

See Create Certificates Locally using openssl <create-certificates-locally-using-openssl> for how to create a private Root certificate and key.

Caution

The default duration for the generated Kubernetes Root CA certificate is 10 years. Replacing the Root certificate is a complex process, so the custom certificate expiry should be set for a long period, if possible. recommends setting the Root certificate with an expiry of at least 5-10 years.

The administrator can also provide values to add to the Kubernetes API server certificate Subject Alternative Name list using the apiserver_cert_sans override parameter.

Use the bootstrap override values <k8s_root_ca_cert> and <k8s_root_ca_key>, as part of the installation procedure to specify the certificate and key for the Kubernetes Root .

<k8s_root_ca_cert>

Specifies the certificate for the Kubernetes Root . The <k8s_root_ca_cert> value is the absolute path of the certificate file. The certificate must be in format and the value must be provided as part of a pair with <k8s_root_ca_key>.

<k8s_root_ca_key>

Specifies the key for the Kubernetes Root . The <k8s_root_ca_key> value is the absolute path of the certificate file. The certificate must be in format and the value must be provided as part of a pair with <k8s_root_ca_cert>.

Note

Ensure the certificates have RSA key length >= 2048 bits. The Release provides a new version of openssl which requires a minimum of 2048-bit keys for RSA for better security / encryption strength.

You can check the key length by running openssl x509 -in <the certificate file> -noout -text and looking for the "Public-Key" in the output. For more information see Create Certificates Locally using openssl <create-certificates-locally-using-openssl>.

For example:

k8s_root_ca_cert: /home/sysadmin/mystarlingx-k8s-rootca-certificate.pem
k8s_root_ca_key: /home/sysadmin/mystarlingx-k8s-rootca-certificate-key.pem

The playbook will not proceed if only one value is provided.

Caution

The default duration for the generated Kubernetes Root certificate is 10 years. Replacing the Root certificate is an involved process so the custom certificate expiry should be as long as possible. We recommend ensuring Root certificate has an expiry of at least 5-10 years.

The administrator can also provide values to add to the Kubernetes API server certificate Subject Alternative Name list using the <apiserver_cert_sans> override parameter.

apiserver_cert_sans

Specifies a list of Subject Alternative Name entries that will be added to the Kubernetes API server certificate. Each entry in the list must be an IP address or domain name. For example:

apiserver_cert_sans:
  - hostname.domain
  - 198.51.100.75

automatically updates this parameter to include IP records for the floating IP and both unit IP addresses. Any names associated with the floating IP address should be added.

Make the K8S Root certificate available to any remote server wanting to connect remotely to the 's Kubernetes API, e.g. through kubectl or Helm. This Kubernetes Root CA certificate should be configured as a trusted on the remote server.

See the step 2.b <security-install-kubectl-and-helm-clients-directly-on-a-host> in Install Kubectl and Helm Clients Directly on a Host.