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Certificate Rotation

This page shows how to enable and configure certificate rotation for the kubelet.

Before you begin

  • Kubernetes version 1.8.0 or later is required

Overview

The kubelet uses certificates for authenticating to the Kubernetes API. By default, these certificates are issued with one year expiration so that they do not need to be renewed too frequently.

Kubernetes 1.8 contains kubelet certificate rotation, a beta feature that will automatically generate a new key and request a new certificate from the Kubernetes API as the current certificate approaches expiration. Once the new certificate is available, it will be used for authenticating connections to the Kubernetes API.

Enabling client certificate rotation

The kubelet process accepts an argument --rotate-certificates that controls if the kubelet will automatically request a new certificate as the expiration of the certificate currently in use approaches. Since certificate rotation is a beta feature, the feature flag must also be enabled with --feature-gates=RotateKubeletClientCertificate=true.

The kube-controller-manager process accepts an argument --experimental-cluster-signing-duration that controls how long certificates will be issued for.

Understanding the certificate rotation configuration

When a kubelet starts up, if it is configured to bootstrap (using the --bootstrap-kubeconfig flag), it will use its initial certificate to connect to the Kubernetes API and issue a certificate signing request. You can view the status of certificate signing requests using:

kubectl get csr

Initially a certificate signing request from the kubelet on a node will have a status of Pending. If the certificate signing requests meets specific criteria, it will be auto approved by the controller manager, then it will have a status of Approved. Next, the controller manager will sign a certificate, issued for the duration specified by the --experimental-cluster-signing-duration parameter, and the signed certificate will be attached to the certificate signing requests.

The kubelet will retrieve the signed certificate from the Kubernetes API and write that to disk, in the location specified by --cert-dir. Then the kubelet will use the new certificate to connect to the Kubernetes API.

As the expiration of the signed certificate approaches, the kubelet will automatically issue a new certificate signing request, using the Kubernetes API. Again, the controller manager will automatically approve the certificate request and attach a signed certificate to the certificate signing request. The kubelet will retrieve the new signed certificate from the Kubernetes API and write that to disk. Then it will update the connections it has to the Kubernetes API to reconnect using the new certificate.

FEATURE STATE: Kubernetes v1.8 beta
This feature is currently in a beta state, meaning:

  • The version names contain beta (e.g. v2beta3).
  • Code is well tested. Enabling the feature is considered safe. Enabled by default.
  • Support for the overall feature will not be dropped, though details may change.
  • The schema and/or semantics of objects may change in incompatible ways in a subsequent beta or stable release. When this happens, we will provide instructions for migrating to the next version. This may require deleting, editing, and re-creating API objects. The editing process may require some thought. This may require downtime for applications that rely on the feature.
  • Recommended for only non-business-critical uses because of potential for incompatible changes in subsequent releases. If you have multiple clusters that can be upgraded independently, you may be able to relax this restriction.
  • Please do try our beta features and give feedback on them! After they exit beta, it may not be practical for us to make more changes.

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