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Hello World Serving

Knative Serving already has a samples page with Hello World services for various languages. In this tutorial, we will build the same with a couple of minor differences:

  1. When building the Docker image, we tag our images with v1, v2, etc. to better track different versions of the service.

  2. When defining the service, we use service-v1.yaml for the first version, service-v2.yaml for the second version etc. Again, to keep track of different service configurations better.

Create a 'Hello World' service

You can either create your 'Hello World' service as described in Knative Serving or take a look at the services we already created in helloworld folder for various languages (csharp, python).

Build and push Docker image

In folder of your language of choice, build and push the container image defined by Dockerfile. Replace {username} with your DockerHub username:

docker build -t {username}/helloworld:v1 .

docker push {username}/helloworld:v1

Deploy the Knative service

Take a look at service-v1.yaml file where we define a Knative service.

After the container is pushed, deploy the Knative service:

kubectl apply -f service-v1.yaml

Check that pods are created and all Knative constructs (service, configuration, revision, route) have been deployed:

kubectl get pod,ksvc,configuration,revision,route

NAME                                                      READY     STATUS    RESTARTS
pod/helloworld-c4pmt-deployment-7fdb5c5dc9-wf2bp   3/3       Running   0

NAME
service.serving.knative.dev/helloworld

NAME
configuration.serving.knative.dev/helloworld

NAME
revision.serving.knative.dev/helloworld-00001

NAME
route.serving.knative.dev/helloworld

(Optional) Install watch

Watch is a command-line tool that runs the specified command repeatedly and displays the results on standard output so you can watch it change over time. It can be useful to watch Knative pods, services, etc. If you're using Mac, you can install watch using homebrew or a similar tool.

To watch pods, Knative service, configuration, revision and route using watch, you can do this:

watch -n 1 kubectl get pod,ksvc,configuration,revision,route

Every 1.0s: kubectl get pod,ksvc,config...

NAME                                                     READY     STATUS    RESTARTS   AGE
pod/helloworld-00001-deployment-b6c485d9f-rm7l4   3/3       Running   0          1m

NAME                                     AGE
service.serving.knative.dev/helloworld   1m

NAME                                           AGE
configuration.serving.knative.dev/helloworld   1m

NAME                                            AGE
revision.serving.knative.dev/helloworld-c4pmt   1m

NAME                                   AGE
route.serving.knative.dev/helloworld   1m

Test the service

Starting with v0.13.0, Knative Serving comes up with an optional Kubernetes job that setups up xip.io as the default domain. This is useful for demo purposes and we're assuming that you have it setup. You can check the installation instructions on Knative Installation page or use the install-serving script we provided.

To test the service, we need to find the IP address of the Istio ingress gateway and the URL of the service.

The IP address of Istio ingress is listed under EXTERNAL_IP:

kubectl get svc istio-ingressgateway -n istio-system

Let's set this EXTERNAL_IP to an ISTIO_INGRESS variable:

export ISTIO_INGRESS=$(kubectl -n istio-system get service istio-ingressgateway -o jsonpath='{.status.loadBalancer.ingress[0].ip}')

The URL of the service follows this format: {service}.{namespace}.example.com. In this case, we have helloworld.default.example.com.

Make a request to your service:

curl http://helloworld.default.$ISTIO_INGRESS.xip.io

Hello v1