Routing across multiple Knative services - Go

This example shows how to map multiple Knative services to different paths under a single domain name using the Istio VirtualService concept. Istio is a general-purpose reverse proxy, therefore these directions can also be used to configure routing based on other request data such as headers, or even to map Knative and external resources under the same domain name.

In this sample, we set up two web services: Search service and Login service, which simply read in an env variable SERVICE_NAME and prints "${SERVICE_NAME} is called". We’ll then create a VirtualService with host example.com, and define routing rules in the VirtualService so that example.com/search maps to the Search service, and example.com/login maps to the Login service.

Prerequisites

  1. A Kubernetes cluster with Knative Serving installed.
  2. Install Docker.
  3. Acquire a domain name.
    • In this example, we use example.com. If you don’t have a domain name, you can modify your hosts file (on Mac or Linux) to map example.com to your cluster’s ingress IP.
  4. Check out the code:
go get -d github.com/knative/docs/docs/serving/samples/knative-routing-go

Setup

Build the application container and publish it to a container registry:

  1. Move into the sample directory:
cd $GOPATH/src/github.com/knative/docs
  1. Set your preferred container registry:
export REPO="gcr.io/<YOUR_PROJECT_ID>"

This example shows how to use Google Container Registry (GCR). You will need a Google Cloud Project and to enable the Google Container Registry API.

  1. Use Docker to build your application container:
docker build \
  --tag "${REPO}/docs/serving/samples/knative-routing-go" \
  --file=docs/serving/samples/knative-routing-go/Dockerfile .
  1. Push your container to a container registry:
docker push "${REPO}/docs/serving/samples/knative-routing-go"
  1. Replace the image reference path with our published image path in the configuration file docs/serving/samples/knative-routing-go/sample.yaml:

    • Manually replace: image: github.com/knative/docs/docs/serving/samples/knative-routing-go with image: <YOUR_CONTAINER_REGISTRY>docs/serving/samples/knative-routing-go

Or

  • Run this command:
   perl -pi -e "s@github.com/knative/docs@${REPO}@g" docs/serving/samples/knative-routing-go/sample.yaml

Deploy the Service

Deploy the Knative Serving sample:

kubectl apply --filename docs/serving/samples/knative-routing-go/sample.yaml

Exploring the Routes

A shared Gateway knative-ingress-gateway is used within Knative service mesh for serving all incoming traffic. You can inspect it and its corresponding Kubernetes service with:

  • Check the shared Gateway:
kubectl get Gateway --namespace knative-serving --output yaml
  • Check the corresponding Kubernetes service for the shared Gateway:
# In Knative 0.2.x and prior versions, the `knative-ingressgateway` service was used instead of `istio-ingressgateway`.
INGRESSGATEWAY=knative-ingressgateway

# The use of `knative-ingressgateway` is deprecated in Knative v0.3.x.
# Use `istio-ingressgateway` instead, since `knative-ingressgateway`
# will be removed in Knative v0.4.
if kubectl get configmap config-istio -n knative-serving &> /dev/null; then
    INGRESSGATEWAY=istio-ingressgateway
fi

kubectl get svc $INGRESSGATEWAY --namespace istio-system --output yaml
  • Inspect the deployed Knative services with:
kubectl get ksvc

You should see 2 Knative services: search-service and login-service.

Access the Services

  1. Find the shared Gateway IP and export as an environment variable:
# In Knative 0.2.x and prior versions, the `knative-ingressgateway` service was used instead of `istio-ingressgateway`.
INGRESSGATEWAY=knative-ingressgateway

# The use of `knative-ingressgateway` is deprecated in Knative v0.3.x.
# Use `istio-ingressgateway` instead, since `knative-ingressgateway`
# will be removed in Knative v0.4.
if kubectl get configmap config-istio -n knative-serving &> /dev/null; then
    INGRESSGATEWAY=istio-ingressgateway
fi

export GATEWAY_IP=`kubectl get svc $INGRESSGATEWAY --namespace istio-system \
    --output jsonpath="{.status.loadBalancer.ingress[*]['ip']}"`
  1. Find the Search service route and export as an environment variable:
export SERVICE_HOST=`kubectl get route search-service --output jsonpath="{.status.domain}"`
  1. Make a curl request to the service:
curl http://${GATEWAY_IP} --header "Host:${SERVICE_HOST}"

You should see: Search Service is called !

  1. Similarly, you can also directly access “Login” service with:
export SERVICE_HOST=`kubectl get route login-service --output jsonpath="{.status.domain}"`
curl http://${GATEWAY_IP} --header "Host:${SERVICE_HOST}"

You should see: Login Service is called !

Apply Custom Routing Rule

  1. Apply the custom routing rules defined in routing.yaml file with:
kubectl apply --filename docs/serving/samples/knative-routing-go/routing.yaml
  1. The routing.yaml file will generate a new VirtualService entry-route for domain example.com. View the VirtualService:
kubectl get VirtualService entry-route --output yaml
  1. Send a request to the Search service and the Login service by using corresponding URIs. You should get the same results as directly accessing these services. _ Get the ingress IP:

    # In Knative 0.2.x and prior versions, the `knative-ingressgateway` service was used instead of `istio-ingressgateway`.
    INGRESSGATEWAY=knative-ingressgateway
    
    # The use of `knative-ingressgateway` is deprecated in Knative v0.3.x.
    # Use `istio-ingressgateway` instead, since `knative-ingressgateway`
    # will be removed in Knative v0.4.
    if kubectl get configmap config-istio -n knative-serving &> /dev/null; then
        INGRESSGATEWAY=istio-ingressgateway
    fi
    
    export GATEWAY_IP=`kubectl get svc $INGRESSGATEWAY --namespace istio-system \
        --output jsonpath="{.status.loadBalancer.ingress[_]['ip']}"`
    * Send a request to the Search service:
    ```shell
    curl http://${GATEWAY_IP}/search --header "Host:example.com"
    ```
    
    * Send a request to the Login service:
    ```shell
    curl http://${GATEWAY_IP}/login --header "Host:example.com"
    ```
    

How It Works

When an external request with host example.com reaches knative-ingress-gateway Gateway, the entry-route VirtualService will check if it has /search or /login URI. If the URI matches, then the host of request will be rewritten into the host of Search service or Login service correspondingly. This resets the final destination of the request. The request with updated host will be forwarded to knative-ingress-gateway Gateway again. The Gateway proxy checks the updated host, and forwards it to Search or Login service according to its host setting.

Object model

Clean Up

To clean up the sample resources:

kubectl delete --filename docs/serving/samples/knative-routing-go/sample.yaml
kubectl delete --filename docs/serving/samples/knative-routing-go/routing.yaml