How to Setup Gunicorn to Serve Python Web Applications
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How to Setup Gunicorn to Serve Python Web Applications

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In this article, we will setup a VPS to serve Python web applications with Gunicorn and Nginx as a reverse proxy. We use Nginx as a reverse proxy instead of serving with Gunicorn directly to prevent DoS attacks on Gunicorn. Using Nginx also results in better performance (with proxy buffering), and results in more requests being handled.

Getting started

This tutorial assumes that you already have a VM with Ubuntu 14.04 or newer installed, updated, and secured.

Install pip, virtualenv:

apt-get install python-pip python-virtualenv

Close port 8080. Gunicorn will be reachable only by Nginx.

iptables -A INPUT -p tcp --destination-port 8080 -j DROP

Create a new folder and configure our application. We'll be using the Flask framework.

mkdir /var/www-folder/
cd /var/www-folder/
virtualenv exampleapp
source exampleapp/bin/activate
cd exampleapp
pip install gunicorn
pip install flask

Create the application file.

nano myapplication.py 

Paste the following inside:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello, Vultr!'

This would produce a simple page saying "Hello, Vultr!" when someone accesses the page. Now, start Gunicorn. Replace x with 2 times the number of your VM's CPU cores.

gunicorn -w x myapplication:app &

Install Nginx and configure the reverse proxy.

deactivate
apt-get install nginx
nano /etc/nginx/sites-enabled/default

Search for the location / { line and replace the content inside the brackets with the following content.

proxy_set_header HOST $host;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_pass http://localhost:8000/;

This configuration instructs Nginx to forward some information (HTTP protocol, remote IP address) along with the actual request to the Gunicorn server. Reload Nginx.

service nginx reload

At this point, your Gunicorn application has been properly configured. You can access it using a web browser at http://your-vps-ip/.

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