Deploy Flask Applications on UnderHost VPS

Flask is a lightweight Python web framework perfect for small to medium applications and microservices. Unlike Django, Flask gives you flexibility without built-in features—you choose your tools. On UnderHost VPS, Flask deploys the same way as Django but with simpler configuration.

Requirements

• UnderHost Cloud VPS
• Python 3.8+
• Nginx and Gunicorn
• Database (optional, your choice)
• SSH access

Project Setup

Create virtual environment:

cd /home/username
python3 -m venv myapp_env
source myapp_env/bin/activate
pip install flask gunicorn

Create Flask app structure:

mkdir myapp
cd myapp
cat > app.py << 'EOF'
from flask import Flask
app = Flask(__name__)

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

if __name__ == '__main__':
    app.run()
EOF

Configure Gunicorn

Test locally with Gunicorn:

gunicorn --bind 127.0.0.1:8000 app:app

Your Flask app is now accessible locally on port 8000.

Nginx Reverse Proxy

Create /etc/nginx/sites-available/myapp:

server {
    listen 80;
    server_name yourdomain.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;
    }
}

Enable and restart:

sudo ln -s /etc/nginx/sites-available/myapp /etc/nginx/sites-enabled/
sudo systemctl restart nginx

Systemd Service

Create /etc/systemd/system/myapp.service:

[Unit]
Description=Flask Gunicorn
After=network.target

[Service]
Type=notify
User=username
WorkingDirectory=/home/username/myapp
ExecStart=/home/username/myapp_env/bin/gunicorn \
    --workers 3 \
    --bind 127.0.0.1:8000 \
    app:app

[Install]
WantedBy=multi-user.target

Start service:

sudo systemctl daemon-reload
sudo systemctl enable myapp
sudo systemctl start myapp

Static Files

Serve CSS, JavaScript, images via Nginx:

# In Nginx config, add:
location /static/ {
    alias /home/username/myapp/static/;
    expires 30d;
}

# In Flask, use:
@app.route('/static/')
def static(filename):
    return send_from_directory('static', filename)

Production Tips

• Use environment variables: os.environ.get('DATABASE_URL') for sensitive config
• Enable HTTPS: Add SSL cert with Let's Encrypt (included in aaPanel/CloudPanel)
• Monitor logs: journalctl -u myapp -f to follow service logs
• Use multiple workers: --workers 3 or more based on CPU cores
• Enable caching: Use Redis or Memcached for session/cache data

Related: Django deployment | Python deployment | Python on CloudPanel

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