Certificate Resources

In cert-manager, the Certificate resource represents a human readable definition of a certificate request that is to be honored by an issuer which is to be kept up-to-date. This is the usual way that you will interact with cert-manager to request signed certificates.

In order to issue any certificates, you’ll need to configure an Issuer resource first.

Creating Certificate Resources

A Certificate resource specifies fields that are used to generate certificate signing requests which are then fulfilled by the issuer type you have referenced. Certificates specify which issuer they want to obtain the certificate from by specifying the certificate.spec.issuerRef field.

A Certificate resource, for the example.com and www.example.com DNS names, spiffe://cluster.local/ns/sandbox/sa/example URI Subject Alternative Name, that is valid for 90 days and renews 15 days before expiry is below. It contains an exhaustive list of all options a Certificate resource may have however only a subset of fields are required as labelled.

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: example-com
  namespace: sandbox
spec:
  # Secret names are always required.
  secretName: example-com-tls
  duration: 2160h # 90d
  renewBefore: 360h # 15d
  subject:
    organizations:
      - jetstack
  # The use of the common name field has been deprecated since 2000 and is
  # discouraged from being used.
  commonName: example.com
  isCA: false
  privateKey:
    algorithm: RSA
    encoding: PKCS1
    size: 2048
  usages:
    - server auth
    - client auth
  # At least one of a DNS Name, URI, or IP address is required.
  dnsNames:
    - example.com
    - www.example.com
  uris:
    - spiffe://cluster.local/ns/sandbox/sa/example
  ipAddresses:
    - 192.168.0.5
  # Issuer references are always required.
  issuerRef:
    name: ca-issuer
    # We can reference ClusterIssuers by changing the kind here.
    # The default value is Issuer (i.e. a locally namespaced Issuer)
    kind: Issuer
    # This is optional since cert-manager will default to this value however
    # if you are using an external issuer, change this to that issuer group.
    group: cert-manager.io

The signed certificate will be stored in a Secret resource named example-com-tls in the same namespace as the Certificate once the issuer has successfully issued the requested certificate.

The Certificate will be issued using the issuer named ca-issuer in the sandbox namespace (the same namespace as the Certificate resource).

Note: If you want to create an Issuer that can be referenced by Certificate resources in all namespaces, you should create a ClusterIssuer resource and set the certificate.spec.issuerRef.kind field to ClusterIssuer.

Note: The renewBefore and duration fields must be specified using a Go time.Duration string format, which does not allow the d (days) suffix. You must specify these values using s, m, and h suffixes instead. Failing to do so without installing the webhook component can prevent cert-manager from functioning correctly #1269.

Note: Take care when setting the renewBefore field to be very close to the duration as this can lead to a renewal loop, where the Certificate is always in the renewal period. Some Issuers set the notBefore field on their issued X.509 certificates before the issue time to fix clock-skew issues, leading to the working duration of a certificate to be less than the full duration of the certificate. For example, Let’s Encrypt sets it to be one hour before issue time, so the actual working duration of the certificate is 89 days, 23 hours (the full duration remains 90 days).

A full list of the fields supported on the Certificate resource can be found in the API reference documentation.

X.509 key usages and extended key usages

cert-manager supports requesting certificates that have a number of custom key usages and extended key usages. Although cert-manager will attempt to honor this request, some issuers will remove, add defaults, or otherwise completely ignore the request. The CA and SelfSigned Issuer will always return certificates matching the usages you have requested.

Unless any number of usages has been set, cert-manager will set the default requested usages of digital signature, key encipherment, and server auth. cert-manager will not attempt to request a new certificate if the current certificate does not match the current key usage set.

An exhaustive list of supported key usages can be found in the API reference documentation.

Temporary Certificates while Issuing

On old GKE versions (1.10.7-gke.1 and below), when requesting certificates using the ingress-shim alongside the ingress-gce ingress controller, ingress-gce required a temporary certificate must be present while waiting for the issuance of a signed certificate. Note that this issue was solved in 1.10.7-gke.2.

# Required for GKE 1.10.7-gke.1 and below.
cert-manager.io/issue-temporary-certificate": "true"

That made sure that a temporary self-signed certificate was present in the Secret. The self-signed certificate was replaced with the signed certificate later on.

Rotation of the private key

By default, the private key won’t be rotated automatically. Using the setting rotationPolicy: Always, the private key Secret associated with a Certificate object can be configured to be rotated as soon as an action triggers the reissuance of the Certificate object (see Actions that will trigger a rotation of the private key below).

With rotationPolicy: Always, cert-manager waits until the Certificate object is correctly signed before overwriting the tls.key file in the Secret.

With this setting, you can expect no downtime if your application can detect changes to the mounted tls.crt and tls.key and reload them gracefully or automatically restart.

If your application only loads the private key and signed certificate once at start up, the new certificate won’t immediately be served by your application, and you will want to either manually restart your pod with kubectl rollout restart, or automate the action by running wave. Wave is a Secret controller that makes sure deployments get restarted whenever a mounted Secret changes.

In the following example, the certificate has been set with rotationPolicy: Always:

apiVersion: cert-manager.io/v1
kind: Certificate
spec:
  secretName: my-cert-tls
  privateKey:
    rotationPolicy: Always # 🔰 Here.

Actions that will trigger a rotation of the private key

Setting the rotationPolicy: Always won’t rotate the private key immediately. In order to rotate the private key, the certificate objects must be reissued. A certificate object is reissued under the following circumstances:

  • when the X.509 certificate is nearing expiry, which is when the Certificate’s status.renewalTime is reached;
  • when a change is made to one of the following fields on the Certificate’s spec: commonName, dnsNames, ipAddresses, uris, emailAddresses, subject, isCA, usages, duration or issuerRef;
  • when a reissuance is manually triggered with the following:
    kubectl cert-manager renew cert-1
    

    Note that the above command requires the kubectl cert-manager plugin.

Deleting the Secret resource associated with a Certificate resource is not a recommended solution for manually rotating the private key. The recommended way to manually rotate the private key is to trigger the reissuance of the Certificate resource with the following command (requires the kubectl cert-manager plugin):

kubectl cert-manager renew cert-1

The rotationPolicy setting

The possible values for rotationPolicy are:

Value Description
Never (default) cert-manager reuses the existing private key on each issuance
Always (recommended) cert-manager regenerates a new private key on each issuance

With rotationPolicy: Never, a private key is only generated if one does not already exist in the target Secret resource (using the tls.key key). All further issuances will re-use this private key. This is the default in order to maintain compatibility with previous releases.

With rotationPolicy: Always, a new private key will be generated each time an action triggers the reissuance of the certificate object (see Actions that will trigger a rotation of the private key above). Note that if the private key secret already exists when creating the certificate object, the existing private key will not be used, since the rotation mechanism also includes the initial issuance.

👉 We recommend that you configure rotationPolicy: Always on your Certificate resources. Rotating both the certificate and the private key simultaneously prevents the risk of issuing a certificate with an exposed private key. Another benefit to renewing the private key regularly is to let you be confident that the private key rotation can be done in case of emergency. More generally, it is a good practice to be rotating the keys as often as possible, reducing the risk associated with compromised keys.

Cleaning up Secrets when Certificates are deleted

By default, cert-manager does not delete the Secret resource containing the signed certificate when the corresponding Certificate resource is deleted. This means that deleting a Certificate won’t take down any services that are currently relying on that certificate, but the certificate will no longer be renewed. The Secret needs to be manually deleted if it is no longer needed.

If you would prefer the Secret to be deleted automatically when the Certificate is deleted, you need to configure your installation to pass the --enable-certificate-owner-ref flag to the controller.

Renewal

cert-manager will automatically renew Certificates. It will calculate when to renew a Certificate based on the issued X.509 certificate’s duration and a ‘renewBefore’ value which specifies how long before expiry a certificate should be renewed.

spec.duration and spec.renewBefore fields on a Certificate can be used to specify an X.509 certificate’s duration and a ‘renewBefore’ value. Default value for spec.duration is 90 days. Some issuers might be configured to only issue certificates with a set duration, so the actual duration may be different. Minimum value for spec.duration is 1 hour and minimum value for spec.renewBefore is 5 minutes. It is also required that spec.duration > spec.renewBefore.

Once an X.509 certificate has been issued, cert-manager will calculate the renewal time for the Certificate. By default this will be 2/3 through the X.509 certificate’s duration. If spec.renewBefore has been set, it will be spec.renewBefore amount of time before expiry. cert-manager will set Certificate’s status.RenewalTime to the time when the renewal will be attempted.