Knative

Google’s Knative project leverages a Kubernetes Cluster Ingress Controller to route requests to apps managed and autoscaled by Knative. At the time of writing, the only available options for Cluster Ingress are Istio and Gloo. This tutorial explains how to get started using Gloo as your Knative Cluster Ingress.

What you’ll need

Steps

  1. First, deploy the Gloo Cluster Ingress and Knative installed on Kubernetes. Knative can be deployed independently, or using glooctl install knative.

  2. Next, we’ll create a sample Go web app to deploy with Knative.

    • 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))
      }
      
    • 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 official 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 as builder
      
      # Copy local code to the container image.
      WORKDIR /go/src/github.com/knative/docs/helloworld
      COPY . .
      
      # Build the helloworld 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
      
      # Copy the binary to the production image from the builder stage.
      COPY --from=builder /go/src/github.com/knative/docs/helloworld/helloworld /helloworld
      
      # Service must listen to $PORT environment variable.
      # This default value facilitates local development.
      ENV PORT 8080
      
      # Run the web service on container startup.
      CMD ["/helloworld"]
      
    • 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:
        runLatest:
          configuration:
            revisionTemplate:
              spec:
                container:
                  image: docker.io/{username}/helloworld-go
                  env:
                    - name: TARGET
                      value: "Go Sample v1"
      
  3. Once the sample code has been created, we’ll build and deploy it

    • 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
      
    • 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
      
    • 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).
    • Run the following command to find the external IP address for the Gloo cluster ingress.

      CLUSTERINGRESS_URL=$(glooctl proxy url --name clusteringress-proxy)
      echo $CLUSTERINGRESS_URL
      http://192.168.99.230:31864
      
    • Run the following command to find the domain URL for your service:

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

      Example:

      NAME                DOMAIN
      helloworld-go       helloworld-go.default.example.com
      
    • 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" ${CLUSTERINGRESS_URL}
      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
      

Great! our Knative ingress is up and running. See https://github.com/knative/docs for more information on using Knative.