1. Introduction

In this tutorial, we'll look at how to scale a Flask application using load balancing. Load balancing is a technique used to distribute network traffic across multiple servers. This improves responsiveness and availability of applications.

You'll learn how to setup a simple Flask application and a load balancer to distribute traffic across multiple instances of the Flask app using Nginx.

Prerequisites:

• Basic understanding of Python programming
• Familiarity with Flask, a Python web framework
• Basic understanding of web servers and networking

2. Step-by-Step Guide

First, we will set up a simple Flask application. Next, we will create multiple instances of this app. Finally, we will use Nginx as a reverse proxy to load balance the traffic among these instances.

1. Flask Application Setup: Flask is a micro web framework written in Python. We will create a simple Flask application which will be served on multiple ports.

2. Creating Multiple Instances: We will run multiple instances of the same Flask application on different ports.

3. Load Balancing with Nginx: Nginx is a web server which can also be used as a reverse proxy, load balancer, and HTTP cache. We will use it to distribute traffic between the instances of our Flask application.

3. Code Examples

Example 1: Creating a Flask Application

# app.py
from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return "Hello, World!"

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

This Flask application has a single route (/) that returns "Hello, World!" when accessed. It is served on port 8080 of your machine.

Example 2: Running Multiple Instances

You can launch multiple instances of this Flask application by changing the port number in the app.run() command. Run each instance in a separate terminal.

Example 3: Configuring Nginx for Load Balancing

# nginx.conf
http {
    upstream flask_apps {
        server localhost:8080;
        server localhost:8081;
        server localhost:8082;
    }

    server {
        listen 80;

        location / {
            proxy_pass http://flask_apps;
        }
    }
}

In this Nginx configuration, we are creating a server block that listens on port 80 and passes incoming requests to one of the Flask apps.

4. Summary

In this tutorial, we covered how to scale a Flask application using load balancing. We learned how to set up a simple Flask app, run multiple instances of it, and use Nginx as a load balancer.

Next, you can learn more about Nginx and its advanced load balancing algorithms, or explore how to set up a load balancer on a cloud platform like AWS or GCP.

5. Practice Exercises

1. Exercise 1: Create a Flask application with multiple routes and apply load balancing.
2. Exercise 2: Use a different load balancing algorithm available in Nginx.
3. Exercise 3: Deploy the load balanced Flask application on a cloud platform.

Solutions:

1. A Flask application with multiple routes can be created similar to the provided example. The load balancing can be done the same way as shown in the tutorial.
2. Nginx supports multiple load balancing methods like least connections, IP Hash, etc. These can be applied by modifying the nginx.conf file.
3. Deployment on a cloud platform involves creating a VM instance, installing necessary software, and setting up the network. The steps will vary based on the platform.