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.

Prerequisites

  • 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

While you can clone all of the code from this directory, hello world apps are generally more useful if you build them step-by-step. The following instructions recreate the source files from this folder.

  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
  1. Install the express package:
   npm install express --save
  1. 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);
   });
  1. 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"
     }
   }
  1. 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" ]
  1. 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:
     runLatest:
       configuration:
         revisionTemplate:
           spec:
             container:
               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
  1. 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
  1. 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).
  2. 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
  1. 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
  1. 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