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Securing Ingress Resources

A common use-case for cert-manager is requesting TLS signed certificates to secure your ingress resources. This can be done by simply adding annotations to your Ingress resources and cert-manager will facilitate creating the Certificate resource for you. A small sub-component of cert-manager, ingress-shim, is responsible for this.

How It Works

The sub-component ingress-shim watches Ingress resources across your cluster. If it observes an Ingress with annotations described in the Supported Annotations section, it will ensure a Certificate resource with the name provided in the tls.secretName field and configured as described on the Ingress exists in the Ingress's namespace. For example:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    # add an annotation indicating the issuer to use.
    cert-manager.io/cluster-issuer: nameOfClusterIssuer
  name: myIngress
  namespace: myIngress
spec:
  rules:
  - host: example.com
    http:
      paths:
      - pathType: Prefix
        path: /
        backend:
          service:
            name: myservice
            port:
              number: 80
  tls: # < placing a host in the TLS config will determine what ends up in the cert's subjectAltNames
  - hosts:
    - example.com
    secretName: myingress-cert # < cert-manager will store the created certificate in this secret.

Supported Annotations

You can specify the following annotations on Ingress resources in order to trigger Certificate resources to be automatically created:

  • cert-manager.io/issuer: the name of an Issuer to acquire the certificate required for this Ingress. The Issuer must be in the same namespace as the Ingress resource.

  • cert-manager.io/cluster-issuer: the name of a ClusterIssuer to acquire the certificate required for this Ingress. It does not matter which namespace your Ingress resides, as ClusterIssuers are non-namespaced resources.

  • cert-manager.io/issuer-kind: the kind of the external issuer resource, for example AWSPCAIssuer. This is only necessary for out-of-tree issuers.

  • cert-manager.io/issuer-group: the API group of the external issuer controller, for example awspca.cert-manager.io. This is only necessary for out-of-tree issuers.

  • kubernetes.io/tls-acme: "true": this annotation requires additional configuration of the ingress-shim see below. Namely, a default Issuer must be specified as arguments to the ingress-shim container.

  • acme.cert-manager.io/http01-ingress-class: this annotation allows you to configure the ingress class that will be used to solve challenges for this ingress. Customizing this is useful when you are trying to secure internal services, and need to solve challenges using a different ingress class to that of the ingress. If not specified and the acme-http01-edit-in-place annotation is not set, this defaults to the ingress class defined in the Issuer resource.

  • acme.cert-manager.io/http01-edit-in-place: "true": this controls whether the ingress is modified 'in-place', or a new one is created specifically for the HTTP01 challenge. If present, and set to "true", the existing ingress will be modified. Any other value, or the absence of the annotation assumes "false". This annotation will also add the annotation "cert-manager.io/issue-temporary-certificate": "true" onto created certificates which will cause a temporary certificate to be set on the resulting Secret until the final signed certificate has been returned. This is useful for keeping compatibility with the ingress-gce component.

  • cert-manager.io/common-name: (optional) this annotation allows you to configure spec.commonName for the Certificate to be generated.

  • cert-manager.io/duration: (optional) this annotation allows you to configure spec.duration field for the Certificate to be generated.

  • cert-manager.io/renew-before: (optional) this annotation allows you to configure spec.renewBefore field for the Certificate to be generated.

  • cert-manager.io/usages: (optional) this annotation allows you to configure spec.usages field for the Certificate to be generated. Pass a string with comma-separated values i.e "key agreement,digital signature, server auth"

  • cert-manager.io/revision-history-limit: (optional) this annotation allows you to configure spec.revisionHistoryLimit field to limit the number of CertificateRequests to be kept for a Certificate. Minimum value is 1. If unset all CertificateRequests will be kept.

  • cert-manager.io/private-key-algorithm: (optional) this annotation allows you to configure spec.privateKey.algorithm field to set the algorithm for private key generation for a Certificate. Valid values are RSA, ECDSA and Ed25519. If unset an algorithm RSA will be used.

  • cert-manager.io/private-key-encoding: (optional) this annotation allows you to configure spec.privateKey.encoding field to set the encoding for private key generation for a Certificate. Valid values are PKCS1 and PKCS8. If unset an algorithm PKCS1 will be used.

  • cert-manager.io/private-key-size: (optional) this annotation allows you to configure spec.privateKey.size field to set the size of the private key for a Certificate. If algorithm is set to RSA, valid values are 2048, 4096 or 8192, and will default to 2048 if not specified. If algorithm is set to ECDSA, valid values are 256, 384 or 521, and will default to 256 if not specified. If algorithm is set to Ed25519, size is ignored.

  • cert-manager.io/private-key-rotation-policy: (optional) this annotation allows you to configure spec.privateKey.rotationPolicy field to set the rotation policy of the private key for a Certificate. Valid values are Never and Always. If unset a rotation policy Never will be used.

Optional Configuration

The ingress-shim sub-component is deployed automatically as part of installation.

If you would like to use the old kube-lego kubernetes.io/tls-acme: "true" annotation for fully automated TLS, you will need to configure a default Issuer when deploying cert-manager. This can be done by adding the following --set when deploying using Helm:

--set ingressShim.defaultIssuerName=letsencrypt-prod \
   --set ingressShim.defaultIssuerKind=ClusterIssuer \
   --set ingressShim.defaultIssuerGroup=cert-manager.io

Or by adding the following arguments to the cert-manager deployment podTemplate container arguments.

- --default-issuer-name=letsencrypt-prod
  - --default-issuer-kind=ClusterIssuer
  - --default-issuer-group=cert-manager.io

In the above example, cert-manager will create Certificate resources that reference the ClusterIssuer letsencrypt-prod for all Ingresses that have a kubernetes.io/tls-acme: "true" annotation.

Issuers configured via annotations have a preference over the default issuer. If a default issuer is configured via CLI flags and a cert-manager.io/cluster-issuer or cert-manager.io/issuer annotation also has been added to an Ingress, the created Certificate will refer to the issuer configured via annotation.

For more information on deploying cert-manager, read the installation guide.

Troubleshooting

If you do not see a Certificate resource being created after applying the ingress-shim annotations check that at least cert-manager.io/issuer or cert-manager.io/cluster-issuer is set. If you want to use kubernetes.io/tls-acme: "true" make sure to have checked all steps above and you might want to look for errors in the cert-manager pod logs if not resolved.