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Enabling auto-TLS certs

If you install and configure cert-manager, you can configure Knative to automatically obtain new TLS certificates and renew existing ones for Knative Services. To learn more about using secure connections in Knative, see Configuring HTTPS with TLS certificates.

Before you begin

The following must be installed on your Knative cluster:

Automatic TLS provision mode

Knative supports the following Auto TLS modes:

  1. Using DNS-01 challenge

    In this mode, your cluster needs to be able to talk to your DNS server to verify the ownership of your domain.

    • Provision Certificate per namespace is supported when using DNS-01 challenge mode.

      • This is the recommended mode for faster certificate provision.
      • In this mode, a single Certificate will be provisioned per namespace and is reused across the Knative Services within the same namespace.
    • Provision Certificate per Knative Service is supported when using DNS-01 challenge mode.

      • This is the recommended mode for better certificate isolation between Knative Services.
      • In this mode, a Certificate will be provisioned for each Knative Service.
      • The TLS effective time is longer as it needs Certificate provision for each Knative Service creation.
  2. Using HTTP-01 challenge

    • In this type, your cluster does not need to be able to talk to your DNS server. You must map your domain to the IP of the cluser ingress.
    • When using HTTP-01 challenge, a certificate will be provisioned per Knative Service.
    • HTTP-01 does not support provisioning a certificate per namespace.

Enabling Auto TLS

  1. Create and add the ClusterIssuer configuration file to your Knative cluster to define who issues the TLS certificates, how requests are validated, and which DNS provider validates those requests.

    • ClusterIssuer for DNS-01 challenge: use the cert-manager reference to determine how to configure your ClusterIssuer file.

      For example, the following ClusterIssuer file named letsencrypt-issuer is configured for the Let's Encrypt CA and Google Cloud DNS. The Let's Encrypt account info, required DNS-01 challenge type, and Cloud DNS provider info is defined under spec.

      apiVersion: cert-manager.io/v1
      kind: ClusterIssuer
      metadata:
        name: letsencrypt-dns-issuer
      spec:
        acme:
          server: https://acme-v02.api.letsencrypt.org/directory
          # This will register an issuer with LetsEncrypt.  Replace
          # with your admin email address.
          email: test-email@knative.dev
          privateKeySecretRef:
            # Set privateKeySecretRef to any unused secret name.
            name: letsencrypt-dns-issuer
          solvers:
          - dns01:
              cloudDNS:
                # Set this to your GCP project-id
                project: $PROJECT_ID
                # Set this to the secret that we publish our service account key
                # in the previous step.
                serviceAccountSecretRef:
                  name: cloud-dns-key
                  key: key.json
      
    • ClusterIssuer for HTTP-01 challenge

      To apply the ClusterIssuer for HTTP01 challenge:

      1. Create a YAML file using the following template:

        apiVersion: cert-manager.io/v1
        kind: ClusterIssuer
        metadata:
          name: letsencrypt-http01-issuer
        spec:
          acme:
            privateKeySecretRef:
              name: letsencrypt
            server: https://acme-v02.api.letsencrypt.org/directory
            solvers:
            - http01:
               ingress:
                 class: istio
        
      2. Apply the YAML file by running the command:

        kubectl apply -f <filename>.yaml
        
        Where <filename> is the name of the file you created in the previous step.

  2. Ensure that the ClusterIssuer is created successfully:

    kubectl get clusterissuer <cluster-issuer-name> -o yaml
    

    Result: The Status.Conditions should include Ready=True.

DNS-01 challenge only: Configure your DNS provider

If you choose to use DNS-01 challenge, configure which DNS provider is used to validate the DNS-01 challenge requests.

Instructions about configuring cert-manager, for all the supported DNS providers, are provided in DNS01 challenge providers and configuration instructions.

Note that DNS-01 challenges can be used to either validate an individual domain name or to validate an entire namespace using a wildcard certificate like *.my-ns.example.com.

Install net-certmanager-controller deployment

  1. Determine if net-certmanager-controller is already installed by running the following command:

    kubectl get deployment net-certmanager-controller -n knative-serving
    
  2. If net-certmanager-controller is not found, run the following command:

    kubectl apply -f https://github.com/knative/net-certmanager/releases/download/knative-v1.7.0/release.yaml
    

Provisioning certificates per namespace (wildcard certificates)

Warning

Provisioning a certificate per namespace only works with DNS-01 challenge. This component cannot be used with HTTP-01 challenge.

The per-namespace certificate manager uses namespace labels to select which namespaces should have a certificate applied. For more details on namespace selectors, see the Kubernetes documentation.

Prior to release 1.0, the fixed label networking.knative.dev/disableWildcardCert: true was used to disable certificate generation for a namespace. In 1.0 and later, other labels such as kubernetes.io/metadata.name may be used to select or restrict namespaces.

To enable certificates for all namespaces except those with the networking.knative.dev/disableWildcardCert: true label, use the following command:

kubectl patch --namespace knative-serving configmap config-network -p '{"data": {"namespace-wildcard-cert-selector": "{\"matchExpressions\": [{\"key\":\"networking.knative.dev/disableWildcardCert\", \"operator\": \"NotIn\", \"values\":[\"true\"]}]}"}}'

This selects all namespaces where the label value is not in the set "true".

Configure config-certmanager ConfigMap

Update your config-certmanager ConfigMap in the knative-serving namespace to reference your new ClusterIssuer.

  1. Run the following command to edit your config-certmanager ConfigMap:

    kubectl edit configmap config-certmanager -n knative-serving
    
  2. Add the issuerRef within the data section:

    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: config-certmanager
      namespace: knative-serving
      labels:
        networking.knative.dev/certificate-provider: cert-manager
    data:
      issuerRef: |
        kind: ClusterIssuer
        name: letsencrypt-http01-issuer
    

    issueRef defines which ClusterIssuer is used by Knative to issue certificates.

  3. Ensure that the file was updated successfully:

    kubectl get configmap config-certmanager -n knative-serving -o yaml
    

Turn on Auto TLS

Update the config-network ConfigMap in the knative-serving namespace to enable auto-tls and specify how HTTP requests are handled:

  1. Run the following command to edit your config-network ConfigMap:

    kubectl edit configmap config-network -n knative-serving
    
  2. Add the auto-tls: Enabled attribute under the data section:

    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: config-network
      namespace: knative-serving
    data:
       ...
       auto-tls: Enabled
       ...
    
  3. Configure how HTTP and HTTPS requests are handled in the http-protocol attribute.

    By default, Knative ingress is configured to serve HTTP traffic (http-protocol: Enabled). Now that your cluster is configured to use TLS certificates and handle HTTPS traffic, you can specify whether or not any HTTP traffic is allowed.

    Supported http-protocol values:

    • Enabled: Serve HTTP traffic.
    • Disabled: Rejects all HTTP traffic.
    • Redirected: Responds to HTTP request with a 302 redirect to ask the clients to use HTTPS.
    data:
      http-protocol: Redirected
    

    Example:

    apiVersion: v1
    kind: ConfigMap
    metadata:
      name: config-network
      namespace: knative-serving
    data:
      ...
      auto-tls: Enabled
      http-protocol: Redirected
      ...
    

    Note

    When using HTTP-01 challenge, http-protocol field has to be set to Enabled to make sure HTTP-01 challenge requests can be accepted by the cluster.

  4. Ensure that the file was updated successfully:

    kubectl get configmap config-network -n knative-serving -o yaml
    

Congratulations! Knative is now configured to obtain and renew TLS certificates. When your TLS certificate is active on your cluster, your Knative services will be able to handle HTTPS traffic.

Verify Auto TLS

  1. Run the following comand to create a Knative Service:

    kubectl apply -f https://raw.githubusercontent.com/knative/docs/main/docs/serving/autoscaling/autoscale-go/service.yaml
    
  2. When the certificate is provisioned (which could take up to several minutes depending on the challenge type), you should see something like:

    NAME               URL                                           LATESTCREATED            LATESTREADY              READY   REASON
    autoscale-go       https://autoscale-go.default.{custom-domain}   autoscale-go-6jf85 autoscale-go-6jf85       True  
    

    Note that the URL will be https in this case.

Disable Auto TLS per service or route

If you have Auto TLS enabled in your cluster, you can choose to disable Auto TLS for individual services or routes by adding the annotation networking.knative.dev/disable-auto-tls: true.

Using the previous autoscale-go example:

  1. Edit the service using kubectl edit service.serving.knative.dev/autoscale-go -n default and add the annotation:

     apiVersion: serving.knative.dev/v1
     kind: Service
     metadata:
       annotations:
        ...
         networking.knative.dev/disable-auto-tls: "true"
        ...
    
  2. The service URL should now be http, indicating that AutoTLS is disabled:

    NAME           URL                                          LATEST               AGE     CONDITIONS   READY   REASON
    autoscale-go   http://autoscale-go.default.1.arenault.dev   autoscale-go-dd42t   8m17s   3 OK / 3     True
    
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