Rotating admin cluster CA certificates

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Google Distributed Cloud use certificates and private keys to authenticate communication between Kubernetes system components in an admin cluster. When you create an admin cluster, new certificate authority (CA) certificates are created, and these root certificates are used to issue additional leaf certificates for Kubernetes system components.

This guide applies only to rotation of admin cluster CA certificates. For user clusters, see Rotating user cluster CA certificates.

There are three CA certificates used by the Kubernetes system in an admin cluster:

• The etcd CA certificate secures communication from the Kubernetes API server to the etcd replicas and also communication between etcd replicas. This certificate is self-signed.

• The cluster CA certificate secures communication between the Kubernetes API server and all internal Kubernetes API clients, for example, the kubelet, the controller manager, and the scheduler. This certificate is self-signed.

• The front-proxy CA certificate secures communication with aggregated APIs. This certificate is self-signed.

You can use gkectl to trigger a certificate rotation. During a rotation, gkectl replaces the core system CA certificates for the admin cluster with newly generated certificates. Then it distributes the new CA certificates, leaf certificates, and private keys to admin cluster system components. The rotation happens incrementally, so that system components can continue to communicate during the rotation. Note, however, that workloads and nodes are restarted during the rotation.

Without rotation, CA certificates and control-plane certificates will expire five years from the date the cluster was created. The control plane certificates are automatically rotated during a cluster upgrade, but the CAs are not automatically rotated. This means a CA rotation must be performed at least once every five years, in addition to regular version upgrades.

Limitations

• Note the following limitation with advanced clusters:

  • Version 1.31: CA rotation isn't supported on advanced clusters.
  • Version 1.32 and higher: CA rotation is supported on advanced clusters but there are some minor differences noted where applicable in this document.

• CA certificate rotation limited to the etcd, cluster, and front-proxy certificates mentioned previously.

• CA certificate rotation is limited to certificates issued automatically by Google Distributed Cloud. It does not update certificates issued manually by an administrator, even if those certificates are signed by the system CAs.

• CA certificate rotation restarts the Kubernetes API server, other control-plane processes, and each node in the admin cluster multiple times. Each stage of a rotation progresses similarly to a cluster upgrade. While the admin cluster and the user clusters managed by the admin cluster do remain operational during a certificate rotation, you should expect that workloads in the admin cluster will be restarted and rescheduled. You should also expect brief periods of downtime for the admin cluster control plane and user cluster control plane.

• You must update the admin cluster kubeconfig file in the middle of a certificate rotation and again after the rotation completes. This is because the old cluster certificate is revoked, and the credentials in the kubeconfig file will no longer work.

• Once initiated, a CA certificate rotation cannot be rolled back.

• A CA certificate rotation might take considerable time to complete, depending on the size of the cluster.

• The certificate rotation process can be resumed by re-running the same command if it is interrupted. However, you must ensure that there is only one rotation command running at a time.

Start the rotation

To start the certificate rotation, run the following command:

gkectl update credentials certificate-authorities rotate \
    --admin-cluster \
    --config ADMIN_CLUSTER_CONFIG \
    --kubeconfig ADMIN_CLUSTER_KUBECONFIG

Replace the following:

• ADMIN_CLUSTER_CONFIG: the path of the admin cluster configuration file

• ADMIN_CLUSTER_KUBECONFIG: the path of the admin cluster kubeconfig file

The behavior of the command differs depending on whether advanced cluster is enabled:

gkectl update credentials certificate-authorities update-kubeconfig \
  --admin-cluster \
  --config ADMIN_CLUSTER_CONFIG \
  --kubeconfig ADMIN_CLUSTER_KUBECONFIG

gkectl update credentials certificate-authorities rotate \
  --admin-cluster \
  --complete \
  --config ADMIN_CLUSTER_CONFIG \
  --kubeconfig ADMIN_CLUSTER_KUBECONFIG

gkectl update credentials certificate-authorities update-kubeconfig \
  --admin-cluster \
  --config ADMIN_CLUSTER_CONFIG \
  --kubeconfig ADMIN_CLUSTER_KUBECONFIG

Beginning CA rotation with generated CA
...
Successfully rotated CA for admin cluster. The kubeconfig file
"/home/ubuntu/kubeconfig" has been updated.
Done rotating certificate-authorities

Distribute the new kubeconfig file

Distribute the new admin cluster kubeconfig file to all cluster users.