docs/doc/source/security/kubernetes/kubernetes-certificates-f4196d7cae9c.rst

Kubernetes Certificates

For Kubernetes, HTTPS is always enabled for both internal and external endpoints. Kubernetes automatically creates all of its client and server certificates used internally and signs them with a Kubernetes Root .

Note

External access to the kube-apiserver API endpoint goes through a HAproxy frontend, which uses the Rest API/GUI certificate.

Kubernetes certificates include:

• Kubernetes Root Certificate
• Cluster admin client certificate
• kube-controller-manager client certificate
• kube-scheduler client certificate
• kube-apiserver server certificate
• kube-apiserver's kubelet client certificate
• kubelet client certificate

Kubernetes Root CA Certificate

The Kubernetes Root certificate signs all the other Kubernetes certificates. This is also the certificate various components use to verify server and client certificates signed by the Kubernetes Root certificate. For example, applications running in pods use Kubernetes Root certificate embedded in service account token to verify the kube-apiserver's server certificate when it makes calls to the kube-apiserver.

By default, the Kubernetes Root is automatically generated at installation time.

If required, you can externally generate a Root certificate and key, and configure it as the Kubernetes Root during installation. See kubernetes-root-ca-certificate. This certificate is only used for internal access. External access goes through HAproxy, which uses the REST API/GUI certificate, issued by the Platform Issuer (system-local-ca). For more information about how to customize the Platform Issuer, see https://docs.starlingx.io/deploy_install_guides/release/ansible_bootstrap_configs.html.

Warning

The Kubernetes must be a Root and not an intermediate . The issuer for external connections, Platform Issuer (system-local-ca) supports intermediate including multi-layered ones.

In a system, by default, the subclouds are deployed with the same Kubernetes Root and Platform Issuer (system-local-ca) as the System Controller. The Root public certificate from the Platform Issuer (system-local-ca) whether auto-generated or specified, needs to be configured as a trusted by the external clients connecting to Cloud Platform’s Kubernetes API endpoint (example, via a remotely installed kubectl client). This certificate is stored in a K8s secret and can be retrieved using the following command:

kubectl get secret system-local-ca -n cert-manager -o=jsonpath='{.data.ca\.crt}' | base64 --decode

For internal clients, the public certificate of Kubernetes Root should be configured as trusted. It can be found at /etc/kubernetes/pki/ca.crt.

Kubernetes Root certificate and corresponding private key are stored in file system:

• /etc/kubernetes/pki/ca.crt
• /etc/kubernetes/pki/ca.key

Updating/Renewing the Kubernetes Root is a complex process, because it is not only the Root certificate that needs to be updated, but also all the other Kubernetes certificates signed by it need to be regenerated and updated. See manual-kubernetes-root-ca-certificate-update-8e9df2cd7fb9 or kubernetes-root-ca-certificate-update-cloud-orchestration-a627f9d02d6d for information on how to update the Kubernetes Root certificate.

Cluster admin client certificate

This is the client certificate signed by Kubernetes Root and embedded in the /etc/kubernetes/admin.conf KUBECONFIG file for kubectl. This is used by internal StarlingX services and users logged in via SSH with sys_protected group permissions, to access kubernetes-admin credentials for kubernetes API or CLI commands.

This certificate is monitored and auto-renewed by a cronjob, which runs every day at midnight to check if the expiry date is approaching, and renew the certificate if the expiry date is within 15 days.

Note

If the cronjob certificate renewal fails, a 250.003 alarm will be raised:

• Kubernetes certificates have been renewed but not all services have been updated.

  For this alarm, controller nodes need to lock/unlock for the services to take the new certificates.

• Kubernetes certificates renewal failed.

  For this alarm, the Kubernetes certificates need to be renewed manually, during which services need to restart.

  If this alarm is raised, the administrator should follow the recommended action for the specific alarm.

kube-controller-manager client certificate

This is the client certificate signed by Kubernetes Root and embedded in /etc/kubernetes/controller-manager.conf. It is used by kube-controller-manager pod to identify itself to kube-apiserver.

This certificate is monitored and auto-renewed by a cronjob, which runs every day at midnight to check if the expiry date is approaching, and renew the certificate if the expiry date is within 15 days.

kube-scheduler client certificate

This is the client certificate signed by Kubernetes Root and embedded in /etc/kubernetes/scheduler.conf. It is used by kube-scheduler pod to identify itself to the kube-apiserver.

This certificate is monitored and auto-renewed by a cronjob, which runs every day at midnight to check if the expiry date is approaching, and renew the certificate if the expiry date is within 15 days.

kube-apiserver server certificate

This is the kube-apiserver's serving certificate. Clients connecting to the kube-apiserver will verify this certificate using Kubernetes Root certificate. The certificate and the corresponding private key are stored in file system:

• /etc/kubernetes/pki/apiserver.crt
• /etc/kubernetes/pki/apiserver.key

This certificate is monitored and auto-renewed by a cronjob, which runs every day at midnight to check if the expiry date is approaching, and renew the certificate if the expiry date is within 15 days.

kube-apiserver's kubelet client certificate

kube-apiserver's client certificate for communications with kubelet. kube-apiserver identifies itself with this certificate when it connects to kubelet. The certificate and the corresponding private keys are stored in file system:

• /etc/kubernetes/pki/apiserver-kubelet-client.crt
• /etc/kubernetes/pki/apiserver-kubelet-client.key

This certificate is monitored and auto-renewed by a cronjob, which runs every day at midnight to check if the expiry date is approaching, and renew the certificate if the expiry date is within 15 days.

kubelet client certificate

This is the kubelet’s client certificate (with private key in it). kubelet identifies itself with this certificate when it connects to kube-apiserver. kubelet has Kubernetes Root certificate in /etc/kubernetes/kubelet.conf to verify peer certificates.

The certificate and its corresponding private key are store in file system as one file:

• /var/lib/kubelet/pki/kubelet-client-current.pem

Kubelet is configured to auto-renew this certificate.

front-proxy-client certificate

Client certificates signed by front-proxy Root certificate. It is used by apiserver/aggregator to connect to aggregated apiserver(extension APIserver).

front-proxy-ca certificate

The front-proxy Root certificate. front-proxy certificates are required only if you run kube-proxy to support an extension API server.