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 generated 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/v1alpha2
kind: Certificate
metadata:
  name: example-com
  namespace: sandbox
spec:
  # Secret names are always required.
  secretName: example-com-tls
  duration: 2160h # 90d
  renewBefore: 360h # 15d
  organization:
  - jetstack
  # The use of the common name field has been deprecated since 2000 and is
  # discouraged from being used.
  commonName: example.com
  isCA: false
  keySize: 2048
  keyAlgorithm: rsa
  keyEncoding: pkcs1
  usages:
    - server auth
    - client auth
  # At least one of a DNS Name, URI, or IP address is required.
  dnsNames:
  - example.com
  - www.example.com
  uriSANs:
  - 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 x509 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

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 and is determined on an issuer by issuer basis. 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 usages set.

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

Temporary Certificates whilst Issuing

When requesting certificates using ingress-shim, the component ingress-gce, if used, requires that a temporary certificate is present while waiting for issuance of a signed certificate when serving. To facilitate this, if the annotation "cert-manager.io/issue-temporary-certificate": "true" is present on the certificate, a self signed temporary certificate will be present on the Secret until it is overwritten once the signed certificate has been issued.

Configuring private key rotation

WARNING: This feature requires enabling the ExperimentalCertificateControllers feature gate by passing the --feature-gates=ExperimentalCertificateControllers=true flag to the controller component, or adding --set featureGates=ExperimentalCertificateControllers=true when deploying using the Helm chart.

When a certificate is re-issued for any reason, including because it is nearing expiry, when a change to the spec is made or a re-issuance is manually triggered, cert-manager supports configuring the ‘private key rotation policy’ to either always re-use the existing private key (the default behavior) or to regenerate a new private key on each issuance (the recommended behavior).

This is configured using the spec.privateKey.rotationPolicy like so:

apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: my-cert
  ...
spec:
  secretName: my-cert-tls
  dnsNames:
  - example.com
  privateKey:
    rotationPolicy: Always

There are two supported rotation policies:

• Never (default): a private key is only generated if one does not already exist in the target Secret resource (using the tls.key key). All further issuance’s will re-use this private key. This is the default in order to maintain compatibility with previous releases.
• Always: a new private key will be generated each time a new certificate is issued. It is recommended you configure this rotationPolicy on your Certificate resources as it is good practice to rotate private keys when a certificate is renewed.

Some Issuer types may disallow re-using private keys. If this is the case, you must explicitly configure the rotationPolicy for each of your Certificates accordingly.

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.