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Hello World - Node.js sample

A simple web app written in Node.js that you can use for testing. It reads in an env variable TARGET and prints "Hello World: ${TARGET}!". If TARGET is not specified, it will use "NOT SPECIFIED" 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.

Create a new directory and initalize npm. You can accept the defaults, but change the entry point to app.js to be consistent with the sample code here.

npm init

package name: (helloworld-nodejs)
version: (1.0.0)
description:
entry point: (index.js) app.js
test command:
git repository:
keywords:
author:
license: (ISC) Apache-2.0

Install the express package:
```
npm install express --save
```

Create a new file named app.js and paste the following code:

const express = require('express');
const app = express();

app.get('/', function (req, res) {
  console.log('Hello world received a request.');

  var target = process.env.TARGET || 'NOT SPECIFIED';
  res.send('Hello world: ' + target);
});

var port = 8080;
app.listen(port, function () {
  console.log('Hello world listening on port',  port);
});

Modify the package.json file to add a start command to the scripts section:

{
  "name": "knative-serving-helloworld",
  "version": "1.0.0",
  "description": "",
  "main": "app.js",
  "scripts": {
    "start": "node app.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "Apache-2.0"
}

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.

FROM node:8

# Create app directory
WORKDIR /usr/src/app

# Install app dependencies
# A wildcard is used to ensure both package.json AND package-lock.json are copied
# where available (npm@5+)
COPY package*.json ./

RUN npm install
# If you are building your code for production
# RUN npm install --only=production

# Bundle app source
COPY . .

EXPOSE 8080
CMD [ "npm", "start" ]

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.

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

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 -f 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).

To find the URL and IP address for your service, use kubectl get ing to list the ingress points in the cluster. It may take a few seconds for the ingress point to be created.

kubectl get ing

NAME                        HOSTS                                       ADDRESS        PORTS     AGE
helloworld-nodejs-ingress   helloworld-nodejs.default.demo-domain.com   35.232.134.1   80        1m

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.demo-domain.com" http://{IP_ADDRESS}
Hello World: NOT SPECIFIED
```

Removing the sample app deployment

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

kubectl delete -f service.yaml

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