1. Developing a basic Python or NodeJs Application

Python Flask ApplicationNodeJs Express Application

Build a Python Flask App

1.1. Create a python virtual environment

As a best practice create a Virtual Environment to get started. In terminal, run the following command:
```
pip install virtualenv
virtualenv venv
```
Once the virtualenv is created, source into the venv by running the following command:
```
source venv/bin/activate
```
You will see the prompt change to (venv)$.

1.2. Install flask library

Since we are building a flask app make sure to install the flask library, by running the following command:
```
pip install flask
```

1.3. Create a python app

Create an app.py file by running the following command:
```
touch app.py
```

Open the app.py in your favourite code editor.

Import the flask module
```
from flask import Flask
```
Set app context
```
app = Flask(__name__)
```

Define a route for /

@app.route('/')
def index():
    return "<h1 align='center'>Hello World from Python Flask!</h1>"

Finally set the flask run

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=8080, debug=True, use_reloader=True)

Your app.py file should look something like this:

app.py

from flask import Flask

app = Flask(__name__)

@app.route('/')
def index():
    return "<h1 align='center'>Hello World from Python Flask!</h1>"

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=8080, debug=True, use_reloader=True)

Save the file.

1.4. Run the App

Back to terminal, run the following command to start the application and check whether it works
```
python app.py
```

You will see output similar to the following:

* Serving Flask app "app" (lazy loading)
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: on
* Running on http://0.0.0.0:8080/ (Press CTRL+C to quit)
* Restarting with stat
* Debugger is active!
* Debugger PIN: 812*299*939

Visit http://0.0.0.0:8080/ on your browser or run the following command:
```
curl http://0.0.0.0:8080
```

You will see output similar to the following:

<h1 align='center'>Hello World from Python Flask!</h1>

If you see Hello World message, congrats you have successfully built the basic flask application.

Build a NodeJs Express App

1.1. Initialize Node Environment

Initialize a new project by running the following command:
```
npm init
```

1.2. Install Express library

Since we are building an Express app make sure to install the Express library by running the following command:
```
npm install express
```
A package.json file will be created in the root directory of your project.

1.3. Set npm start command

Add app.js to the package.json scripts section:

"scripts": {
    "start": "node app.js",
    "test": "echo \"Error: no test specified\" && exit 1"
},

1.4. Create a NodeJs Express app

Create an app.js file by running the following command:
```
touch app.js
```

Open the app.js in your favourite code editor.

Import the express module
```
const express = require('express');
```
Set app context
```
const app = express();
```
Set port on which you want the app to listen
```
const port = 3000;
```

Define a route for /

app.get('/', (req, res) => {
    res.send("<h1 align='center'>Hello World from NodeJs Express!</h1>");
});

Finally set the express run

app.listen(port, () => {
    console.log(`Example app listening on port ${port}!`);
});

Your app.js file should look something like this:

app.js

const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
    res.send("<h1 align='center'>Hello World from NodeJs Express!</h1>");
});

app.listen(port, () => {
    console.log(`Example app listening on port ${port}!`);
});

Save the file.

1.5. Run the App

Back to terminal, run the following command to start the application and check whether it works
```
npm start
```
You will see output similar to the following:
```
Example app listening on port 3000!
```
Visit http://0.0.0.0:3000/ on your browser or run the following command:
```
curl http://0.0.0.0:3000
```

You will see output similar to the following:

<h1 align='center'>Hello World from Python Flask!</h1>

If you see Hello World message, congrats you have successfully built the basic express application.