How to Deploy a Flask App (Python) with Gunicorn

This guide shows how to put a Flask application online with OpenPanel. The app runs in its own Python container, and OpenPanel's web server forwards your domain to it, with a free SSL certificate.

How It Works​

• Your code lives in the domain's folder, e.g. /var/www/html/example.com/.
• OpenPanel starts an official python container with that folder as the working directory.
• On every start, the container can run pip install -r requirements.txt and then your startup command.
• The web server (Nginx, Apache, OpenResty or OpenLiteSpeed) proxies https://example.com to the port your app listens on.

Step 1: Prepare the App​

A minimal project:

example.com/
├── app.py
└── requirements.txt

app.py:

from flask import Flask

app = Flask(__name__)

@app.route("/")
def index():
    return "Hello from Flask on OpenPanel!"

requirements.txt:

Flask==3.0.3
gunicorn==23.0.0

Flask's built-in server (app.run()) is for development only. In production, run the app with Gunicorn.

Step 2: Add the Domain and Upload the Code​

1. Add the domain in OpenPanel → Domains (see Add a new domain) and point its DNS to the server.
2. Upload your files to the domain's folder with the File Manager, FTP, or skip this step and deploy from Git in the next step.

Step 3: Create the Python Application​

Go to OpenPanel → Websites → Install App → Setup Python Application and fill in:

Click Start Installation. When it's done, open https://example.com.

app:app means module app (the file app.py) and the Flask object named app. If your project uses an application factory, wrap it in single quotes: gunicorn --bind 0.0.0.0:8000 'app:create_app()'. Don't use double quotes in the startup command.

Step 4: Connect a Database​

Create a database and user in OpenPanel → MySQL → Database Wizard (or PostgreSQL). Inside containers, databases are reached by service name, not localhost:

Example with SQLAlchemy:

import os
from flask_sqlalchemy import SQLAlchemy

app.config["SQLALCHEMY_DATABASE_URI"] = os.environ.get(
    "DATABASE_URL", "mysql+pymysql://dbuser:dbpass@mysql:3306/dbname"
)
db = SQLAlchemy(app)

Add Flask-SQLAlchemy and PyMySQL (or psycopg2-binary for PostgreSQL) to requirements.txt. See connecting to MySQL from applications.

Step 5: Secrets and Environment Variables​

Keep secrets out of your code. Put them in a .env file in the app folder and load it with python-dotenv:

# /var/www/html/example.com/.env
SECRET_KEY=change-me
DATABASE_URL=mysql+pymysql://dbuser:dbpass@mysql:3306/dbname

from dotenv import load_dotenv
load_dotenv()

Don't commit the .env file to Git. Restart the app after changing it.

Managing the App​

Open OpenPanel → Websites → Sites and click Manage next to the app:

• Restart after changing code or settings (Gunicorn doesn't reload automatically).
• Install Packages to edit requirements.txt and run pip.
• Logs to see Gunicorn output and Python tracebacks.
• Overview to change the startup command, Python version and CPU/memory limits.

More details: Python applications.

Troubleshooting​

Related​

• Deploy a Django app
• Deploy a Laravel app
• Host a PHP website