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.
   • If you have configured a custom domain for your Knative installation, we will refer to it as <YOUR_DOMAIN_NAME> in the rest of this document
4. Check out the code:

go get -d github.com/knative/docs/code-samples/serving/knative-routing-go

Setup

To check the domain name, run the following command:

kubectl get cm  -n knative-serving config-domain -o yaml

Then, check the value for data. The domain name should be in the format of <YOUR_DOMAIN_NAME>: "", if it is available.

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

1. Move into the sample directory:

cd $GOPATH/src/github.com/knative/docs

2. Set your preferred container registry:

If you use Google Container Registry (GCR), you will need to enable the GCR API in your GCP project.

export REPO="gcr.io/<YOUR_PROJECT_ID>"

If you use Docker Hub as your docker image registry, replace with your dockerhub username and run the following command:

export REPO="docker.io/<username>"

3. Use Docker to build and push your application container:

# Build and push the container on your local machine.
docker buildx build --platform linux/arm64,linux/amd64 -t "${REPO}/knative-routing-go" --push . -f code-samples/serving/knative-routing-go/Dockerfile

4. Replace the image reference path with our published image path in the configuration file code-samples/serving/knative-routing-go/sample.yaml:

   • Manually replace: image: github.com/knative/docs/code-samples/serving/knative-routing-go with image: ${REPO}/knative-routing-go If you manually changed the .yaml file, you must replace ${REPO} with the correct path on your local machine.

   Or

   • Run this command:

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

Deploy the Service

Deploy the Knative Serving sample:

kubectl apply --filename code-samples/serving/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:

INGRESSGATEWAY=istio-ingressgateway

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:

INGRESSGATEWAY=istio-ingressgateway

export GATEWAY_IP=`kubectl get svc $INGRESSGATEWAY --namespace istio-system \
    --output jsonpath="{.status.loadBalancer.ingress[*]['ip']}"`

2. Find the Search service URL with:

# kubectl get route search-service  --output=custom-columns=NAME:.metadata.name,URL:.status.url
NAME              URL
search-service    http://search-service.default.example.com

3. Make a curl request to the service:

curl http://${GATEWAY_IP} --header "Host:search-service.default.example.com"

You should see: Search Service is called !

4. Similarly, you can also directly access "Login" service with:

curl http://${GATEWAY_IP} --header "Host:login-service.default.example.com"

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 code-samples/serving/knative-routing-go/routing.yaml

If you have configured a custom domain name for your service, please replace all mentions of "example.com" in routing.yaml with "<YOUR_DOMAIN_NAME>" for spec.hosts and spec.http.rewrite.authority.

{% raw %} In addition, you need to verify how your domain template is defined. By default, we use the format of {{.Name}}.{{.Namespace}}, like search-service.default and login-service.default. However, some Knative environments may use other format like {{.Name}}-{{.Namespace}}. You can find out the format by running the command: {% endraw %}

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

{% raw %} Then look for the value for domain-template. If it is {{.Name}}-{{.Namespace}}.{{.Domain}}, you need to change search-service.default into search-service-default and login-service.default into login-service-default as well in routing.yaml. {% endraw %}

2. The routing.yaml file will generate a new VirtualService entry-route for domain example.com or your own domain name. View the VirtualService:

kubectl get VirtualService entry-route --output yaml

3. 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:

   INGRESSGATEWAY=istio-ingressgateway
   
   export GATEWAY_IP=`kubectl get svc $INGRESSGATEWAY --namespace istio-system \
       --output jsonpath="{.status.loadBalancer.ingress[*]['ip']}"`

• Send a request to the Search service:

  curl http://${GATEWAY_IP}/search --header "Host: example.com"

  or

  curl http://${GATEWAY_IP}/search --header "Host: <YOUR_DOMAIN_NAME>"

  for the case using your own domain.

• Send a request to the Login service:

  curl http://${GATEWAY_IP}/login --header "Host: example.com"

  or

  curl http://${GATEWAY_IP}/login --header "Host: <YOUR_DOMAIN_NAME>"

  for the case using your own domain.

How It Works

When an external request with host example.com or your own domain name 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.

Using internal services and "http-protocol": "Redirected"

Using the approach explained in the previous section, services will be available using two entrypoints into the cluster: The original ones provided by Knative Serving (search-service.default.example.com and login-service.default.example.com), as well as the additional entrypoints example.com/search and example.com/login provided by the manually added VirtualService (entry-route).

To make sure your service can only be reached via the manually created VirtualService, you can add the label networking.knative.dev/visibility: cluster-local to the Knative Service definitions, and route traffic over knative-local-gateway.istio-system.svc.cluster.local with a destination address of an internal service, instead of the public ingress one at istio-ingressgateway.istio-system.svc.cluster.local with a destination address of an externally available service.

Using

kubectl label kservice search-service login-service networking.knative.dev/visibility=cluster-local

you label the services as an cluster-local services, removing access via search-service.default.example.com and login-service.default.example.com. After doing so, your previous routing rule will not be routable anymore. Running

kubectl apply --filename code-samples/serving/knative-routing-go/routing-internal.yaml

will replace the custom routing rule with one that uses the knative-local-gateway, enabling access via example.com/search and example.com/login again.

With these changes, you can also use the auto-tls feature in combination with the global setting "http-protocol": "Redirected", which would otherwise try to redirect the entry-route VirtualService requests from HTTP to HTTPS, failing the request.

Clean Up

To clean up the sample resources:

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