Certificate resource

apiVersion: cert-manager.io/v1
kind: Certificate

In cert-manager, the Certificate resource represents a human readable definition of a certificate request. cert-manager uses this input to generate a private key and CertificateRequest resource in order to obtain a signed certificate from an Issuer or ClusterIssuer. The signed certificate and private key are then stored in the specified Secret resource. cert-manager will ensure that the certificate is auto-renewed before it expires and re-issued if requested.

In order to issue any certificates, you'll need to configure an Issuer or ClusterIssuer 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

  # secretTemplate is optional. If set, these annotations and labels will be
  # copied to the Secret named example-com-tls. These labels and annotations will
  # be re-reconciled if the Certificate's secretTemplate changes. secretTemplate
  # is also enforced, so relevant label and annotation changes on the Secret by a
  # third party will be overwriten by cert-manager to match the secretTemplate.
  secretTemplate:
    annotations:
      my-secret-annotation-1: "foo"
      my-secret-annotation-2: "bar"
    labels:
      my-secret-label: foo

  privateKey:
    algorithm: RSA
    encoding: PKCS1
    size: 2048

  # keystores allows adding additional output formats. This is an example for reference only.
  keystores:
    pkcs12:
      create: true
      passwordSecretRef:
        name: example-com-tls-keystore
        key: password
      profile: Modern2023

  duration: 2160h # 90d
  renewBefore: 360h # 15d

  isCA: false
  usages:
    - server auth
    - client auth

  subject:
    organizations:
      - cert-manager

  # Avoid using commonName for DNS names in end-entity (leaf) certificates. Unless you have a specific
  # need for it in your environment, use dnsNames exclusively to avoid issues with commonName.
  # Usually, commonName is used to give human-readable names to CA certificates and can be avoided for
  # other certificates.
  commonName: example.com

  # The literalSubject field is exclusive with subject and commonName. It allows
  # specifying the subject directly as a string. This is useful for when the order
  # of the subject fields is important or when the subject contains special types
  # which can be specified by their OID.
  #
  # literalSubject: "O=jetstack, CN=example.com, 2.5.4.42=John, 2.5.4.4=Doe"

  # At least one of commonName (possibly through literalSubject), dnsNames, uris, emailAddresses, ipAddresses or otherNames is required.
  dnsNames:
    - example.com
    - www.example.com
  uris:
    - spiffe://cluster.local/ns/sandbox/sa/example
  emailAddresses:
    - john.doe@cert-manager.io
  ipAddresses:
    - 192.168.0.5
  # Needs cert-manager 1.14+ and "OtherNames" feature flag
  otherNames:
    # Should only supply oid of ut8 valued types
    - oid: 1.3.6.1.4.1.311.20.2.3 # User Principal Name "OID"
      utf8Value: upn@example.local

  # 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.

If secretTemplate is present, annotations and labels set in this property will be copied over to example-com-tls secret. Both properties are optional.

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.

Target Secret

When a certificate is issued by an intermediate CA and the Issuer can provide the issued certificate's chain, the contents of tls.crt will be the requested certificate followed by the certificate chain.

Additionally, if the Certificate Authority is known, the corresponding CA certificate will be stored in the secret with key ca.crt. For example, with the ACME issuer, the CA is not known and ca.crt will not exist in the Secret. The ca.crt value at the time of issuance can be copied to the trust store of the application that is using the certificate. However, DO NOT directly mount the ca.crt value into the application's trust store, as it will be updated when the certificate is renewed (see Trusting certificates for more details).

cert-manager intentionally avoids adding root certificates to tls.crt, because they are useless in a situation where TLS is being done securely. For more information, see RFC 5246 section 7.4.2 which contains the following explanation:

Because certificate validation requires that root keys be distributed independently, the self-signed certificate that specifies the root certificate authority MAY be omitted from the chain, under the assumption that the remote end must already possess it in order to validate it in any case.

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.

Additional Certificate Output Formats

additionalOutputFormats is a field on the Certificate spec that allows specifying additional supplementary formats of issued certificates and their private key. There are currently two supported additional output formats: CombinedPEM and DER. Both output formats can be specified on the same Certificate.

apiVersion: cert-manager.io/v1
kind: Certificate
spec:
  ...
  secretName: my-cert-tls
  additionalOutputFormats:
  - type: CombinedPEM
  - type: DER

# Results in:

apiVersion: v1
kind: Secret
metadata:
  name: my-cert-tls
type: kubernetes.io/tls
data:
  ca.crt: <PEM CA certificate>
  tls.key: <PEM private key>
  tls.crt: <PEM signed certificate chain>
  tls-combined.pem: <PEM private key + "\n" + PEM signed certificate chain>
  key.der: <DER binary format of private key>

CombinedPEM

The CombinedPEM type will create a new key entry in the resulting Certificate's Secret tls-combined.pem. This entry will contain the PEM encoded private key, followed by at least one new line character, followed by the PEM encoded signed certificate chain-

<private key> + "\n" + <signed certificate chain>

apiVersion: v1
kind: Secret
metadata:
  name: my-cert-tls
type: kubernetes.io/tls
data:
  tls-combined.pem: <PEM private key + "\n" + PEM signed certificate chain>
  ...

DER

The DER type will create a new key entry in the resulting Certificate's Secret key.der. This entry will contain the DER binary format of the private key.

apiVersion: v1
kind: Secret
metadata:
  name: my-cert-tls
type: kubernetes.io/tls
data:
  key.der: <DER binary format of private key>
  ...

Creating Certificate With Name Constraints

Root or Intermediate CA certificates can have name constraints. Name constraints indicates a name space within which all subject names in subsequent certificates in a certification path MUST be located. Checkout https://datatracker.ietf.org/doc/html/rfc5280#section-4.2.1.10 for more details on this.

--feature-gates=NameConstraints=true

To create a CA Certificate with name constraints use the following configuration:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: ca-cert-example
spec:
  secretName: example-ca-key-pair
  isCA: true
  issuerRef:
    name: selfsigned
    kind: ClusterIssuer
  commonName: "example1.com"
  dnsNames:
  - example1.com
  nameConstraints:
    critical: true
    permitted:
      dnsDomains: ["example1.com", "example2.com"]
      ipRanges: ["10.10.0.0/16"]
      emailAddress: ["example@example.org"]
    excluded:
      ipRanges: ["10.10.0.0/24"]

Note that when used with cert-manager's built-in CA and SelfSigned Issuer, the SANs (DNS name, IP address, URI, and email address) are not checked with the certificate's own name constraints, and are not checked with any of name constraints contained in the chain of certificates the certificate belongs to.

The certificate may get issued successfully, but be rejected by clients during TLS handshakes.

Issuance triggers

Reissuance triggered by expiry (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/spec.renewBeforePercentage 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. spec.renewBefore specifies an absolute duration, while spec.renewBeforePercentage computes the effective 'renewBefore' using the actual duration of the issued certificate. Using spec.renewBeforePercentage is recommended to prevent renewal loops in case the actual duration is less than expected. Minimum value for spec.duration is 1 hour and minimum value for effective 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 or spec.renewBeforePercentage has been set, it will be the effective spec.renewBefore amount of time before expiry. cert-manager will set Certificate's status.RenewalTime to the time when the renewal will be attempted.

Reissuance triggered by user actions

A certificate object is reissued under the following circumstances:

• 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; A more detailed explanation can be found on the FAQ page.
• when a reissuance is manually triggered with the following:

  cmctl renew cert-1

  Note that the above command requires cmctl.

cmctl renew cert-1

Issuance behavior: Temporary Certificates while Issuing

When requesting certificates using the ingress-shim, the component ingress-gce, if used, requires that a temporary certificate is present while waiting for the issuance of a signed certificate when serving. To facilitate this, if the following 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.

Adding the following annotation on an ingress will automatically set "issue-temporary-certificate" on the certificate:

acme.cert-manager.io/http01-edit-in-place: "true"

Issuance behavior: 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 the Certificate is reissued (see Issuance triggers).

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.

The rotationPolicy setting

The possible values for rotationPolicy are:

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.

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.

Inner workings diagram for developers

[1] https://cert-manager.io/docs/usage/certificaterequest