Creating a RESTful Service - Go

This sample demonstrates creating and running a simple RESTful service on Knative Serving. The exposed endpoint takes a stock ticker (i.e. stock symbol), then outputs the stock price.

Prerequisites

  1. A Kubernetes cluster with Knative Serving v0.3 or higher installed.
  2. Docker installed locally.
  3. Outbound network access enabled for this Service to make external API requests.
  4. The code checked out locally.
  5. envsubst installed locally. This is installed by the gettext package. If not installed it can be installed by a Linux package manager, or by Homebrew on OS X.
go get -d github.com/knative/docs/docs/serving/samples/rest-api-go

Setup

In order to run an application on Knative Serving a container image must be available to fetch from a container registry. Building and pushing a container image can be accomplished locally using Docker or ko as well as remotely using Knative Build.

This sample uses Docker for both building and pushing.

To build and push to a container registry using Docker:

  1. Move into the sample directory:
cd $GOPATH/src/github.com/knative/docs
  1. Set your preferred container registry endpoint as an environment variable. This sample uses Google Container Registry (GCR):
export REPO="gcr.io/<YOUR_PROJECT_ID>"
  1. Set up your container registry to make sure you are ready to push.

To push to GCR, you need to:

If you are using a different container registry, you will want to follow the registry specific instructions for both setup and authorizing the image push.

  1. Use Docker to build your application container:
docker build \
  --tag "${REPO}/rest-api-go" \
  --file docs/serving/samples/rest-api-go/Dockerfile .
  1. Push your container to a container registry:
docker push "${REPO}/rest-api-go"
  1. Substitute the image reference path in the template with our published image path. The command below substitutes using the ${REPO} variable into a new file called docs/serving/samples/rest-api-go/sample.yaml.
   envsubst < docs/serving/samples/rest-api-go/sample-template.yaml > \
   docs/serving/samples/rest-api-go/sample.yaml

Deploy the Service

Now that our image is available from the container registry, we can deploy the Knative Serving sample:

kubectl apply --filename docs/serving/samples/rest-api-go/sample.yaml

The above command creates a Knative Service within your Kubernetes cluster in the default namespace.

Explore the Service

The Knative Service creates the following child resources:

  • Knative Route
  • Knative Configuration
  • Knative Revision
  • Kubernetes Deployment
  • Kuberentes Service

You can inspect the created resources with the following kubectl commands:

  • View the created Service resource:
kubectl get ksvc stock-service-example --output yaml
  • View the created Route resource:
kubectl get route -l \
"serving.knative.dev/service=stock-service-example" --output yaml
  • View the Kubernetes Service created by the Route
kubectl get service -l \
"serving.knative.dev/service=stock-service-example" --output yaml
  • View the created Configuration resource:
kubectl get configuration -l \
"serving.knative.dev/service=stock-service-example" --output yaml
  • View the Revision that was created by our Configuration:
kubectl get revision -l \
"serving.knative.dev/service=stock-service-example" --output yaml
  • View the Deployment created by our Revision
kubectl get deployment -l \
"serving.knative.dev/service=stock-service-example" --output yaml

Access the Service

To access this service via curl, you need to determine its ingress address. This example assumes you are using the default Ingress Gateway setup for Knative. If you customized your gateway, you will want to adjust the enviornment variables below.

Find Ingress Gateway IP

Cloud Provider

  1. To get the IP address of your Ingress Gateway:
INGRESSGATEWAY=istio-ingressgateway
INGRESSGATEWAY_LABEL=istio

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

Minikube

  1. If your cluster is running outside a cloud provider (for example on Minikube), your services will never get an external IP address, and your INGRESS_IP will be empty. In that case, use the istio hostIP and nodePort as the ingress IP:
export INGRESS_IP=$(kubectl get po --selector $INGRESSGATEWAY_LABEL=ingressgateway --namespace istio-system \
  --output 'jsonpath={.items[0].status.hostIP}'):$(kubectl get svc $INGRESSGATEWAY --namespace istio-system \
  --output 'jsonpath={.spec.ports[?(@.port==80)].nodePort}')
echo $INGRESS_IP

Get Service Hostname

  1. To get the hostname of the Service:
export SERVICE_HOSTNAME=`kubectl get ksvc stock-service-example --output jsonpath="{.status.domain}"`
echo $SERVICE_HOSTNAME

Sending Requests

  1. Now use curl to make a request to the Service:
  • Make a request to the index endpoint:

The curl command below makes a request to the Ingress Gateway IP. The Ingress Gateway uses the host header to route the request to the Service. This example passes the host header to skip DNS configuration. If your cluster has DNS configured, you can simply curl the DNS name instead of the ingress gateway IP.

curl --header "Host:$SERVICE_HOSTNAME" http://${INGRESS_IP}

Response body: Welcome to the stock app!

  • Make a request to the /stock endpoint:
curl --header "Host:$SERVICE_HOSTNAME" http://${INGRESS_IP}/stock

Response body: stock ticker not found!, require /stock/{ticker}

  • Make a request to the /stock endpoint with a ticker parameter:
curl --header "Host:$SERVICE_HOSTNAME" http://${INGRESS_IP}/stock/<ticker>

Response body: stock price for ticker <ticker> is <price>

Next Steps

The traffic splitting example continues from here to walk through creating new Revisions and splitting traffic between multiple Revisions.

Clean Up

To clean up the sample Service:

kubectl delete --filename docs/serving/samples/rest-api-go/sample.yaml