Enabling automatic TLS certificate provisioning

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.

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 islation 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 just need to map your domain to the IP of the cluser ingress.
    • When using HTTP-01 challenge, a certificate will be provisioned per Knative Service. Certificate provision per namespace is not supported when using HTTP-01 challenge.

Before you begin

You must meet the following prerequisites to enable auto TLS:

Enabling Auto TLS

To enable support for Auto TLS in Knative:

Create cert-manager ClusterIssuer

  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:

    • See the generic ClusterIssuer example

    • Also see the DNS01 example

      Example: Cloud DNS ClusterIssuer configuration file:

      The following letsencrypt-issuer named ClusterIssuer file is configured for the Let’s Encrypt CA and Google Cloud DNS. Under spec, the Let’s Encrypt account info, required DNS-01 challenge type, and Cloud DNS provider info defined. For the complete Google Cloud DNS example, see Configuring HTTPS with cert-manager and Google Cloud DNS.

      apiVersion: cert-manager.io/v1alpha2
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: myemail@gmail.com
    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

    Run the following command to apply the ClusterIssuer for HTT01 challenge:

    kubectl apply -f - <<EOF
apiVersion: cert-manager.io/v1alpha2
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
EOF

  2. Ensure that the ClusterIssuer is created successfully:

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

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

Install networking-certmanager deployment

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

    kubectl get deployment networking-certmanager -n knative-serving

  2. If networking-certmanager is not found, run the following command:

    kubectl apply --filename https://github.com/knative/net-certmanager/releases/download/v0.16.0/release.yaml

Install networking-ns-cert component

If you choose to use the mode of provisioning certificate per namespace, you need to install networking-ns-cert components.

  1. Determine if networking-ns-cert deployment is already installed by running the following command:

    kubectl get deployment networking-ns-cert -n knative-serving

  2. If networking-ns-cert deployment is not found, run the following command:

    kubectl apply --filename https://github.com/knative/serving/releases/download/v0.16.0/serving-nscert.yaml

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 --namespace knative-serving

  2. Add the issuerRef within the data section:

    ...
data:
...
  issuerRef: |
    kind: ClusterIssuer
    name: letsencrypt-issuer

    Example:

    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 will be used by Knative to issue certificates.

  3. Ensure that the file was updated successfully:

    kubectl get configmap config-certmanager --namespace knative-serving --output yaml

Turn on Auto TLS

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

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

    kubectl edit configmap config-network --namespace knative-serving

  2. Add the autoTLS: Enabled attribute under the data section:

    ...
data:
...
  autoTLS: Enabled
...

    Example:

    apiVersion: v1
kind: ConfigMap
metadata:
  name: config-network
  namespace: knative-serving
data:
   ...
   autoTLS: Enabled
   ...

  3. Configure how HTTP and HTTPS requests are handled in the httpProtocol attribute.

    By default, Knative ingress is configured to serve HTTP traffic (httpProtocol: 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 httpProtocol 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:
...
  autoTLS: Enabled
...

    Example:

    apiVersion: v1
kind: ConfigMap
metadata:
  name: config-network
  namespace: knative-serving
data:
  ...
  autoTLS: Enabled
  ...
  httpProtocol: Redirected
  ...

    Note: When using HTTP-01 challenge, httpProtocol 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 --namespace knative-serving --output 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/master/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.