How to Deploy a Flask Application on Windows IIS Server: A Complete Guide

Deploying a Flask web application on a Windows IIS Server requires a series of precise configurations. This guide will provide a step-by-step, accurate, and professional approach to getting your Flask app running on IIS using FastCGI and wfastcgi.

Prerequisites

Before you begin, ensure you have:

• Windows Server with IIS installed.
• Administrator access to the server.
• Python 3.x installed from python.org.
• A Flask project ready for deployment.

Step 1: Install Python

Step 2: Set Up Python Virtual Environment

To create an isolated environment for your Flask project:

Open Command Prompt as an administrator.

Navigate to your project directory:

cd c:\path\to\your\project\directory

Create a virtual environment using:

python -m venv venv

Activate the virtual environment:

venv\Scripts\activate

This ensures all dependencies are installed in isolation from system Python.

Step 3: Install Project Dependencies

Once your virtual environment is active, install your Flask app dependencies:

Create or update your requirements.txt file:

pip freeze > requirements.txt

Check and Install dependencies from requirements.txt file. This file includes all the dependencies needed to your project:

pip install -r requirements.txt

This ensures your app has all the necessary packages installed.

Step 4: Install and Configure wfastcgi

Install IIS Features

1. Open Server Manager, and click Add Roles and Features.
2. Under Server Roles, select Web Server (IIS).
3. In Role Services, scroll down to Application Development and check CGI.
4. Complete the installation by clicking Next and Install.

Install and Enable wfastcgi

Now, install and configure wfastcgi, a Python package that allows IIS to communicate with your Flask app via FastCGI:

Install wfastcgi in your virtual environment:

pip install wfastcgi

Enable wfastcgi in IIS:

wfastcgi-enable

This command registers wfastcgi.py as the FastCGI script processor for Python, and you'll receive output similar to the following:

Applied configuration changes to section "system.webServer/fastCgi" for "MACHINE/WEBROOT/APPHOST"

"c:\path\to\python.exe|c:\path\to\wfastcgi.py" can now be used as a FastCGI script processor.

Make note of the scriptProcessor path from the output.

Step 5: Create the web.config File

To link your Flask app with IIS, create a web.config file in the root directory of your Flask project (where main.py is located). Here is an example of a sample flask project structure.

path="*"

verb="*"

modules="FastCgiModule"

scriptProcessor="c:\path\to\python.exe|c:\path\to\wfastcgi.py"

resourceType="Unspecified"

requireAccess="Script" />

Replace the following:

scriptProcessorwith the path you noted earlier.

WSGI_HANDLER with your_main_file_name.app (e.g., if your main file is main.py, it would be main.app).

PYTHONPATH with the path to your project directory.

Step 6: Configure IIS

1. Open IIS Manager and create a new website.
2. In the left pane, right-click Sites and choose Add Website Fill in your site's name, the physical path to your Flask project, and the hostname.
3. Select your newly created website from the list.
4. In the right-hand panel, double-click Configuration Editor.
5. Unlock the system.webServer/fastCgi section to allow configurations for FastCGI.

Step 7: Grant Permissions to IIS_IUSRS

1. Right-click your project folder and select Properties.
2. Go to the Security tab, and click Edit.
3. Add IIS_IUSRS, and grant it Read & Execute permissions.

Step 8: Restart IIS and Test Your Application

Finally, restart IIS to apply all changes:

iisreset

Now, navigate to your server's domain or IP address in a web browser. If everything is set up correctly, your Flask app should load.

Conclusion

Deploying Flask applications on Windows IIS Server using wfastcgi can be challenging but manageable with a step-by-step approach. By ensuring Python, IIS, and Flask are correctly configured, you’ll have a fully functional web apåplication deployed on your Windows Server.