Kubernetes v1.15
stable
Client certificates generated by kubeadm expire after 1 year. This page explains how to manage certificate renewals with kubeadm.
Be familiar with PKI certificates and requirements in Kubernetes.
You should be familiar with PKI certificates and requirements in Kubernetes.
check-expiration
can be used to check certificate expiration.
kubeadm alpha certs check-expiration
The output is similar to this:
CERTIFICATE EXPIRES RESIDUAL TIME EXTERNALLY MANAGED
admin.conf May 15, 2020 13:03 UTC 364d false
apiserver May 15, 2020 13:00 UTC 364d false
apiserver-etcd-client May 15, 2020 13:00 UTC 364d false
apiserver-kubelet-client May 15, 2020 13:00 UTC 364d false
controller-manager.conf May 15, 2020 13:03 UTC 364d false
etcd-healthcheck-client May 15, 2020 13:00 UTC 364d false
etcd-peer May 15, 2020 13:00 UTC 364d false
etcd-server May 15, 2020 13:00 UTC 364d false
front-proxy-client May 15, 2020 13:00 UTC 364d false
scheduler.conf May 15, 2020 13:03 UTC 364d false
The command shows expiration/residual time for the client certificates in the /etc/kubernetes/pki
folder and for the client certificate embedded in the KUBECONFIG files used by kubeadm (admin.conf
, controller-manager.conf
and scheduler.conf
).
Additionally, kubeadm informs the user if the certificate is externally managed; in this case, the user should take care of managing certificate renewal manually/using other tools.
Warning:kubeadm
cannot manage certificates signed by an external CA.
Note:kubelet.conf
is not included in the list above because kubeadm configures kubelet for automatic certificate renewal.
kubeadm
renews all the certificates during control plane upgrade.
This feature is designed for addressing the simplest use cases; if you don’t have specific requirements on certificate renewal and perform Kubernetes version upgrades regularly (less than 1 year in between each upgrade), kubeadm will take care of keeping your cluster up to date and reasonably secure.
Note: It is a best practice to upgrade your cluster frequently in order to stay secure.
If you have more complex requirements for certificate renewal, you can opt out from the default behavior by passing --certificate-renewal=false
to kubeadm upgrade apply
or to kubeadm upgrade node
.
You can renew your certificates manually at any time with the kubeadm alpha certs renew
command.
This command performs the renewal using CA (or front-proxy-CA) certificate and key stored in /etc/kubernetes/pki
.
Warning: If you are running an HA cluster, this command needs to be executed on all the control-plane nodes.
Note:alpha certs renew
uses the existing certificates as the authoritative source for attributes (Common Name, Organization, SAN, etc.) instead of the kubeadm-config ConfigMap. It is strongly recommended to keep them both in sync.
kubeadm alpha certs renew
provides the following options:
The Kubernetes certificates normally reach their expiration date after one year.
--csr-only
can be used to renew certificats with an external CA by generating certificate signing requests (without actually renewing certificates in place); see next paragraph for more information.
It’s also possible to renew a single certificate instead of all.
This section provide more details about how to execute manual certificate renewal using the Kubernetes certificates API.
Caution: These are advanced topics for users who need to integrate their organization’s certificate infrastructure into a kubeadm-built cluster. If the default kubeadm configuration satisfies your needs, you should let kubeadm manage certificates instead.
The Kubernetes Certificate Authority does not work out of the box.
You can configure an external signer such as cert-manager, or you can use the build-in signer.
The built-in signer is part of kube-controller-manager
.
To activate the build-in signer, you pass the --cluster-signing-cert-file
and --cluster-signing-key-file
arguments.
The built-in signer is part of kube-controller-manager
.
To activate the build-in signer, you must pass the --cluster-signing-cert-file
and --cluster-signing-key-file
flags.
If you’re creating a new cluster, you can use a kubeadm configuration file:
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
controllerManager:
extraArgs:
cluster-signing-cert-file: /etc/kubernetes/pki/ca.crt
cluster-signing-key-file: /etc/kubernetes/pki/ca.key
You can create the certificate signing requests for the Kubernetes certificates API with kubeadm alpha certs renew --use-api
.
If you set up an external signer such as [cert-manager][cert-manager], certificate signing requests (CSRs) are automatically approved.
Otherwise, you must manually approve certificates with the kubectl certificate
command.
The following kubeadm command outputs the name of the certificate to approve, then blocks and waits for approval to occur:
sudo kubeadm alpha certs renew apiserver --use-api &
The output is similar to this:
[1] 2890
[certs] certificate request "kubeadm-cert-kube-apiserver-ld526" created
If you set up an external signer, certificate signing requests (CSRs) are automatically approved.
Otherwise, you must manually approve certificates with the kubectl certificate
command. e.g.
kubectl certificate approve kubeadm-cert-kube-apiserver-ld526
The output is similar to this:
certificatesigningrequest.certificates.k8s.io/kubeadm-cert-kube-apiserver-ld526 approved
You can view a list of pending certificates with kubectl get csr
.
This section provide more details about how to execute manual certificate renewal using an external CA.
To better integrate with external CAs, kubeadm can also produce certificate signing requests (CSRs). A CSR represents a request to a CA for a signed certificate for a client. In kubeadm terms, any certificate that would normally be signed by an on-disk CA can be produced as a CSR instead. A CA, however, cannot be produced as a CSR.
You can pass in a directory with --csr-dir
to output the CSRs to the specified location.
If --csr-dir
is not specified, the default certificate directory (/etc/kubernetes/pki
) is used.
Both the CSR and the accompanying private key are given in the output. After a certificate is signed, the certificate and the private key must be copied to the PKI directory (by default /etc/kubernetes/pki
).
A CSR represents a request to a CA for a signed certificate for a client.
You can create certificate signing requests with kubeadm alpha certs renew --csr-only
.
Both the CSR and the accompanying private key are given in the output; you can pass in a directory with --csr-dir
to output the CSRs to the specified location.
Certificates can be renewed with kubeadm alpha certs renew --csr-only
.
As with kubeadm init
, an output directory can be specified with the --csr-dir
flag.
To use the new certificates, copy the signed certificate and private key into the PKI directory (by default /etc/kubernetes/pki
)
A CSR contains a certificate’s name, domain(s), and IPs, but it does not specify usages.
A CSR contains a certificate’s name, domains, and IPs, but it does not specify usages. It is the responsibility of the CA to specify the correct cert usages when issuing a certificate.
openssl
this is done with the openssl ca
command.cfssl
you specify usages in the config fileAfter a certificate is signed using your preferred method, the certificate and the private key must be copied to the PKI directory (by default /etc/kubernetes/pki
).
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