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 "{{< branch >}}" https://github.com/knative/docs knative-docs
cd knative-docs/docs/serving/samples/hello-world/helloworld-nodejs

Before you begin

• A Kubernetes cluster with Knative installed and DNS configured. 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}!\n`);
   });
   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 lightweight Node.js 12 image.
   # https://hub.docker.com/_/node
   FROM node:12-slim
   # 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 .dockerignore file to ensure that any files related to a local build do not affect the container that you build for deployment.

   Dockerfile
   README.md
   node_modules
   npm-debug.log

7. 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/v1
   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 URL for your service, use

   kubectl get ksvc helloworld-nodejs  --output=custom-columns=NAME:.metadata.name,URL:.status.url
   NAME                URL
   helloworld-nodejs   http://helloworld-nodejs.default.1.2.3.4.xip.io

5. Now you can make a request to your app and see the result. Replace the URL below with the URL returned in the previous command.

   curl http://helloworld-nodejs.default.1.2.3.4.xip.io
   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