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Using custom domains for Knative services with Service Mesh

By default, Knative services have a fixed domain format:

 <application_name>-<namespace>.<openshift_cluster_domain>

You can customize the domain for your Knative service by configuring the service as a private service and creating the required Service Mesh resources.

Prerequisites

Setting cluster availability to cluster-local

By default, Knative services are published to a public IP address. Being published to a public IP address means that Knative services are public applications, and have a publicly accessible URL.

Publicly accessible URLs are accessible from outside of the cluster. However, developers may need to build back-end services that are only be accessible from inside the cluster, known as private services. Developers can label individual services in the cluster with the serving.knative.dev/visibility=cluster-local label to make them private.

Procedure

  • Set the visibility for your service by adding the serving.knative.dev/visibility=cluster-local label:

    $ oc label ksvc <service_name> serving.knative.dev/visibility=cluster-local
Verification

  • Check that the URL for your service is now in the format http://<service_name>.<namespace>.svc.cluster.local, by entering the following command and reviewing the output:

    $ oc get ksvc
    Example output
    NAME            URL                                                                         LATESTCREATED     LATESTREADY       READY   REASON
hello           http://hello.default.svc.cluster.local                                      hello-tx2g7       hello-tx2g7       True

Creating necessary Service Mesh resources

Procedure

  1. Create an Istio gateway to accept traffic.

    1. Create a YAML file, and copy the following YAML into it:

      apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: default-gateway
spec:
  selector:
    istio: ingressgateway
  servers:
  - port:
      number: 80
      name: http
      protocol: HTTP
    hosts:
    - "*"

    2. Apply the YAML file:

      $ oc apply -f <filename>

  2. Create an Istio VirtualService object to rewrite the host header.

    1. Create a YAML file, and copy the following YAML into it:

      apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: hello
spec:
  hosts:
  - custom-ksvc-domain.example.com
  gateways:
  - default-gateway
  http:
  - rewrite:
      authority: hello.default.svc (1)
    route:
    - destination:
        host: hello.default.svc (1)
        port:
          number: 80
      1 Your Knative service in the format <service_name>.<namespace>.svc.

    2. Apply the YAML file:

      $ oc apply -f <filename>

  3. Create an Istio ServiceEntry object. This is required for OpenShift Serverless because Kourier is outside of the service mesh.

    1. Create a YAML file, and copy the following YAML into it:

      apiVersion: networking.istio.io/v1alpha3
kind: ServiceEntry
metadata:
  name: hello.default.svc
spec:
  hosts:
  - hello.default.svc (1)
  location: MESH_EXTERNAL
  endpoints:
  - address: kourier-internal.knative-serving-ingress.svc
  ports:
  - number: 80
    name: http
    protocol: HTTP
  resolution: DNS
      1 Your Knative service in the format <service_name>.<namespace>.svc.

    2. Apply the YAML file:

      $ oc apply -f <filename>

  4. Create an OpenShift Container Platform route that points to the VirtualService object.

    1. Create a YAML file, and copy the following YAML into it:

      apiVersion: route.openshift.io/v1
kind: Route
metadata:
  name: hello
  namespace: istio-system (1)
spec:
  host: custom-ksvc-domain.example.com
  port:
    targetPort: 8080
  to:
    kind: Service
    name: istio-ingressgateway
1 The OpenShift Container Platform route must be created in the same namespace as the ServiceMeshControlPlane. In this example, the ServiceMeshControlPlane is deployed in the istio-system namespace.

  1. Apply the YAML file:

    $ oc apply -f <filename>

Accessing a service using your custom domain

Procedure

  1. Access the custom domain by using the Host header in a curl request. For example:

    $ curl -H "Host: custom-ksvc-domain.example.com" http://<ip_address>

    where <ip_address> is the IP address that the OpenShift Container Platform ingress router is exposed to.

    Example output
    Hello OpenShift!

Additional resources