Securing Gateway Resources

FEATURE STATE: cert-manager 1.5 [alpha]

cert-manager can generate TLS certificates for Gateway resources. This is configured by adding annotations to a Gateway and is similar to the process for Securing Ingress Resources.

The Gateway resource is part of the Gateway API, a set of CRDs that you install on your Kubernetes cluster and which provide various improvements over the Ingress API.

The Gateway resource holds the TLS configuration, as illustrated in the following diagram (source: https://gateway-api.sigs.k8s.io):

Note that cert-manager only supports setting up the TLS configuration on the Gateway resource when the Gateway is configured to terminate the TLS connection. There is still uncertainty around how the HTTPRoute TLS configuration should be used (see the discussion about TLS interaction between HTTPRoute and Gateway) and no existing implementation supports the TLS pass-through mode in which the HTTPRoute contains the TLS configuration and terminates the connection (see the feature request for supporting spec.tls in HTTPRoute for Istio).

kubectl kustomize "github.com/kubernetes-sigs/gateway-api/config/crd?ref=v0.4.1" | kubectl apply -f -

kubectl rollout restart deployment cert-manager -n cert-manager

The annotations cert-manager.io/issuer or cert-manager.io/cluster-issuer tell cert-manager to create a Certificate for a Gateway. For example, the following Gateway will trigger the creation of a Certificate with the name example-com-tls:

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: Gateway
metadata:
  name: example
  annotations:
    cert-manager.io/issuer: foo
spec:
  gatewayClassName: foo
  listeners:
    - name: http
      hostname: example.com
      port: 443
      protocol: HTTPS
      allowedRoutes:
        namespaces:
          from: All
      tls:
        mode: Terminate
        certificateRefs:
          - name: example-com-tls

A few moments later, cert-manager will create a Certificate. The Certificate is named after the Secret name example-com-tls. The dnsNames field is set with the hostname field from the Gateway spec.

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: example-com-tls
spec:
  issuerRef:
    name: my-issuer
    kind: Issuer
    group: cert-manager.io
  dnsNames:
    - example.com # ✅ Copied from the `hostname` field.
  secretName: example-com-tls

Use cases

Generate TLS certs for selected TLS blocks

cert-manager skips any listener block that cannot be used for generating a Certificate. For a listener block to be used for creating a Certificate, it must meet the following requirements:

In the following example, the first three listener blocks will not be used to generate Certificate resources:

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: Gateway
metadata:
  annotations:
    cert-manager.io/issuer: my-issuer
spec:
  listeners:
    # ❌  Missing "tls" block, the following listener is skipped.
    - hostname: example.com

    # ❌  Missing "hostname", the following listener is skipped.
    - tls:
        certificateRefs:
          - name: example-com-tls
            kind: Secret"
            group: core

    # ❌  "mode: Passthrough" is not supported, the following listener is skipped.
    - hostname: example.com
      tls:
        mode: Passthrough
        certificateRefs:
          - name: example-com-tls
            kind: Secret
            group: core

    # ✅  The following listener is valid.
    - hostname: foo.example.com # ✅ Required.
      port: 443
      protocol: HTTPS
      allowedRoutes:
        namespaces:
          from: All
      tls:
        mode: Terminate # ✅ Required. "Terminate" is the only supported mode.
        certificateRefs:
          - name: example-com-tls # ✅ Required.
            kind: Secret  # ✅ Required. "Secret" is the only valid value.
            group: core # ✅ Required. "core" is the only valid value.

cert-manager has skipped over the first three listener blocks and has created a single Certificate named example-com-tls for the last listener block:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: example-com-tls
spec:
  issuerRef:
    name: my-issuer
    kind: Issuer
    group: cert-manager.io
  dnsNames:
    - foo.example.com
  secretName: example-com-tls

Two listeners with the same Secret name

The same Secret name can be re-used in multiple TLS blocks, regardless of the hostname. Let us imagine that you have these two listeners:

apiVersion: gateway.networking.k8s.io/v1alpha2
kind: Gateway
metadata:
  name: example
  annotations:
    cert-manager.io/issuer: my-issuer
spec:
  gatewayClassName: foo
  listeners:
    # Listener 1.
    - hostname: example.com
      port: 443
      protocol: HTTPS
      routes:
        kind: HTTPRoute
        parentRefs:
          - name: example
            kind: Gateway
      tls:
        mode: Terminate
        certificateRefs:
          - name: example-com-tls
            kind: Secret
            group: core

    # Listener 2: Same Secret name as Listener 1, with a different hostname.
    - hostname: *.example.com
      port: 443
      protocol: HTTPS
      routes:
        kind: HTTPRoute
        parentRefs:
          - name: example
            kind: Gateway
      tls:
        mode: Terminate
        certificateRefs:
          - name: example-com-tls
            kind: Secret
            group: core

    # Listener 3: also same Secret name, except the hostname is also the same.
    - hostname: *.example.com
      port: 8443
      protocol: HTTPS
      routes:
        kind: HTTPRoute
        parentRefs:
          - name: example
            kind: Gateway
      tls:
        mode: Terminate
        certificateRefs:
          - name: example-com-tls
            kind: Secret
            group: core

   # Listener 4: different Secret name.
    - hostname: site.org
      port: 443
      protocol: HTTPS
      routes:
        kind: HTTPRoute
        parentRefs:
          - name: example
            kind: Gateway
      tls:
        mode: Terminate
        certificateRefs:
          - name: site-org-tls
            kind: Secret
            group: core

cert-manager will create two Certificates since two Secret names are used: example-com-tls and site-org-tls. Note the Certificate's dnsNames contains a single occurrence of *.example.com for both listener 2 and 3 (the hostname values are de-duplicated).

The two Certificates look like this:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: example-com-tls
spec:
  issuerRef:
    name: my-issuer
    kind: Issuer
    group: cert-manager.io
  dnsNames:
    - example.com # From listener 1.
    - *.example.com # From listener 2 and 3.
  secretName: example-com-tls
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: site-org-tls
spec:
  issuerRef:
    name: my-issuer
    kind: Issuer
    group: cert-manager.io
  dnsNames:
    - site.org # From listener 4.
  secretName: site-org-tls

Supported Annotations

If you are migrating to Gateway resources from Ingress resources, be aware that there are some differences between the annotations for Ingress resources versus the annotations for Gateway resources.

The Gateway resource supports the following annotations for generating Certificate resources:

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

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

• cert-manager.io/issuer-kind: the kind of the external issuer resource, for example AWSPCACIssuer. 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.

• 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.