A simple web app written in Go that you can use for testing. It reads in an env variable TARGET and prints Hello ${TARGET}!. If TARGET is not specified, it will use World as the TARGET.

Follow the steps below to create the sample code and then deploy the app to your cluster. You can also download a working copy of the sample, by running the following commands:

git clone -b "release-0.6" https://github.com/knative/docs knative-docs
cd knative-docs/serving/samples/hello-world/helloworld-go

Before you begin

• A Kubernetes cluster with Knative installed. Follow the installation instructions if you need to create one.
• Docker installed and running on your local machine, and a Docker Hub account configured (we'll use it for a container registry).

Recreating the sample code

1. Create a new file named helloworld.go and paste the following code. This code creates a basic web server which listens on port 8080:

   package main
   
   import (
     "fmt"
     "log"
     "net/http"
     "os"
   )
   
   func handler(w http.ResponseWriter, r *http.Request) {
     log.Print("Hello world received a request.")
     target := os.Getenv("TARGET")
     if target == "" {
       target = "World"
     }
     fmt.Fprintf(w, "Hello %s!\n", target)
   }
   
   func main() {
     log.Print("Hello world sample started.")
   
     http.HandleFunc("/", handler) 
   
     port := os.Getenv("PORT")
     if port == "" {
       port = "8080"
     }
   
     log.Fatal(http.ListenAndServe(fmt.Sprintf(":%s", port), nil))
   }

2. In your project directory, create a file named Dockerfile and copy the code block below into it. For detailed instructions on dockerizing a Go app, see Deploying Go servers with Docker.

   # Use the offical Golang image to create a build artifact.
   # This is based on Debian and sets the GOPATH to /go.
   # https://hub.docker.com/_/golang
   FROM golang:1.12 as builder
   
   # Copy local code to the container image.
   WORKDIR /go/src/github.com/knative/docs/helloworld
   COPY . .
   
   # Build the command inside the container.
   # (You may fetch or manage dependencies here,
   # either manually or with a tool like "godep".)
   RUN CGO_ENABLED=0 GOOS=linux go build -v -o helloworld
   
   # Use a Docker multi-stage build to create a lean production image.
   # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
   FROM alpine
   RUN apk add --no-cache ca-certificates
   
   # Copy the binary to the production image from the builder stage.
   COPY --from=builder /go/src/github.com/knative/docs/helloworld/helloworld /helloworld
   
   # Run the web service on container startup.
   CMD ["/helloworld"]
   

3. Create a new file, service.yaml and copy the following service definition into the file. Make sure to replace {username} with your Docker Hub username.

   apiVersion: serving.knative.dev/v1alpha1
   kind: Service
   metadata:
     name: helloworld-go
     namespace: default
   spec:
     template:
       spec:
         containers:
           - image: docker.io/{username}/helloworld-go
             env:
               - name: TARGET
                 value: "Go Sample v1"

Building and deploying the sample

Once you have recreated the sample code files (or used the files in the sample folder) you're ready to build and deploy the sample app.

1. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

   # Build the container on your local machine
   docker build -t {username}/helloworld-go .
   
   # Push the container to docker registry
   docker push {username}/helloworld-go

2. After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in service.yaml matches the container you built in the previous step. Apply the configuration using kubectl:

   kubectl apply --filename service.yaml

3. Now that your service is created, Knative will perform the following steps:

   • Create a new immutable revision for this version of the app.
   • Network programming to create a route, ingress, service, and load balance for your app.
   • Automatically scale your pods up and down (including to zero active pods).

4. Run the following command to find the external IP address for your service. The ingress IP for your cluster is returned. If you just created your cluster, you might need to wait and rerun the command until your service gets asssigned an external IP address.

   # 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

   Example:

   NAME                     TYPE           CLUSTER-IP     EXTERNAL-IP      PORT(S)                                      AGE
   xxxxxxx-ingressgateway   LoadBalancer   10.23.247.74   35.203.155.229   80:32380/TCP,443:32390/TCP,32400:32400/TCP   2d

5. Run the following command to find the domain URL for your service:

   kubectl get ksvc helloworld-go  --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain

   Example:

    NAME                DOMAIN
    helloworld-go       helloworld-go.default.example.com

6. Test your app by sending it a request. Use the following curl command with the domain URL helloworld-go.default.example.com and EXTERNAL-IP address that you retrieved in the previous steps:

   curl -H "Host: helloworld-go.default.example.com" http://{EXTERNAL_IP_ADDRESS}

   Example:

   curl -H "Host: helloworld-go.default.example.com" http://35.203.155.229
   Hello Go Sample v1!

   Note: Add -v option to get more detail if the curl command failed.

Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

kubectl delete --filename service.yaml