How to Use Nginx with Flask: Simple Setup Guide

To use nginx with a Flask app, run Flask with a production server like gunicorn and configure nginx as a reverse proxy to forward client requests to the Flask server. This setup improves performance and allows nginx to handle static files and security.

Syntax

This is the basic nginx server block syntax to proxy requests to a Flask app running on localhost port 8000. It listens on port 80 and forwards requests to the Flask server.

• listen 80;: Nginx listens on HTTP port 80.
• server_name example.com;: Your domain or IP.
• location /: Matches all requests.
• proxy_pass http://127.0.0.1:8000;: Forwards requests to Flask server.
• proxy_set_header: Passes client info to Flask.

nginx

server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://127.0.0.1:8000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

Example

This example shows a simple Flask app served by gunicorn on port 8000, with nginx configured as a reverse proxy on port 80. Requests to http://localhost/ are forwarded to Flask.

bash

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

@app.route('/')
def hello():
    return "Hello from Flask behind Nginx!"

# Run gunicorn server (in terminal):
gunicorn -w 4 -b 127.0.0.1:8000 app:app

# Nginx config (e.g., /etc/nginx/sites-available/flask_app):
server {
    listen 80;
    server_name localhost;

    location / {
        proxy_pass http://127.0.0.1:8000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }
}

# After saving nginx config, reload nginx:
sudo nginx -s reload

Output

When visiting http://localhost/ in a browser, the page shows:
Hello from Flask behind Nginx!

Common Pitfalls

Common mistakes when using nginx with Flask include:

• Not running Flask with a production server like gunicorn or uwsgi, which can cause poor performance.
• Forgetting to set proxy_set_header directives, which can break client IP detection.
• Not reloading nginx after changing configuration.
• Binding Flask to 127.0.0.1 but trying to access it externally without nginx.

Example of a wrong config missing headers:

nginx

server {
    listen 80;
    server_name example.com;

    location / {
        proxy_pass http://127.0.0.1:8000;
        # Missing proxy_set_header lines causes client info loss
    }
}

# Corrected config includes proxy_set_header directives as shown in the Syntax section.

Quick Reference

Tips for using nginx with Flask:

• Always run Flask with gunicorn or uwsgi in production.
• Use nginx as a reverse proxy to handle client requests and serve static files.
• Set proper proxy_set_header directives to forward client info.
• Reload nginx after config changes with sudo nginx -s reload.
• Test locally before deploying to production.

Key Takeaways

Use gunicorn or uwsgi to serve Flask in production behind nginx.

Configure nginx as a reverse proxy with proxy_pass to forward requests.

Set proxy_set_header directives to preserve client information.

Reload nginx after any configuration changes.

Test the full setup locally before deploying.