Hello World - Node.js

A simple web app written in Node.js 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-nodejs

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).
  • Node.js installed and configured.

Recreating the sample code

  1. Create a new directory and initialize npm:

    npm init
    
    package name: (helloworld-nodejs)
    version: (1.0.0)
    description:
    entry point: (index.js)
    test command:
    git repository:
    keywords:
    author:
    license: (ISC) Apache-2.0
  2. Install the express package:

    npm install express
  3. Create a new file named index.js and paste the following code:

    const express = require("express");
    const app = express();
    
    app.get("/", (req, res) => {
      console.log("Hello world received a request.");
    
      const target = process.env.TARGET || "World";
      res.send(`Hello ${target}!`);
    });
    
    const port = process.env.PORT || 8080;
    app.listen(port, () => {
      console.log("Hello world listening on port", port);
    });
    
  4. Modify the package.json file to add a start command to the scripts section:

    {
      "name": "knative-serving-helloworld",
      "version": "1.0.0",
      "description": "Simple hello world sample in Node",
      "main": "index.js",
      "scripts": {
        "start": "node index.js"
      },
      "author": "",
      "license": "Apache-2.0",
      "dependencies": {
        "express": "^4.16.4"
      }
    }
  5. In your project directory, create a file named Dockerfile and copy the code block below into it. For detailed instructions on dockerizing a Node.js app, see Dockerizing a Node.js web app.

    # Use the official Node.js 10 image.
    # https://hub.docker.com/_/node
    FROM node:10
    
    # Create and change to the app directory.
    WORKDIR /usr/src/app 
    
    # Copy application dependency manifests to the container image.
    # A wildcard is used to ensure both package.json AND package-lock.json are copied.
    # Copying this separately prevents re-running npm install on every code change.
    COPY package*.json ./
     
    # Install production dependencies.
    RUN npm install --only=production
    
    # Copy local code to the container image.
    COPY . .
    
    # Run the web service on container startup.
    CMD [ "npm", "start" ]
  6. 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-nodejs
     namespace: default
    spec:
     template:
       spec:
         containers:
         - image: docker.io/{username}/helloworld-nodejs
           env:
             - name: TARGET
               value: "Node.js 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-nodejs .
    
    # Push the container to docker registry
    docker push {username}/helloworld-nodejs
  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. To find the IP address for your service, use these commands to get the ingress IP for your cluster. If your cluster is new, it may take sometime for the service to get 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
    
    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. To find the URL for your service, use

    kubectl get ksvc helloworld-nodejs  --output=custom-columns=NAME:.metadata.name,DOMAIN:.status.domain
    NAME                DOMAIN
    helloworld-nodejs   helloworld-nodejs.default.example.com
    
  6. Now you can make a request to your app to see the result. Replace {IP_ADDRESS} with the address you see returned in the previous step.

    curl -H "Host: helloworld-nodejs.default.example.com" http://{IP_ADDRESS}
    Hello Node.js Sample v1!

Removing the sample app deployment

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

kubectl delete --filename service.yaml