How to Ensure Flask Includes Prefix Set by Kubernetes Ingress: A Step-by-Step Guide

As a developer, you’re probably no stranger to the challenges of deploying Flask applications on Kubernetes. One common pain point is ensuring that Flask includes the prefix set by the Kubernetes Ingress controller. In this article, we’ll walk you through a step-by-step guide on how to achieve this, and by the end of it, you’ll be a master of prefixing your way to a smoothly running Flask app on Kubernetes!

What’s the Problem?

Before we dive into the solution, let’s first understand the problem at hand. When you deploy a Flask application on Kubernetes, the Ingress controller sets a prefix for your application. This prefix is usually in the format of `/api/v1` or `/app`. However, Flask by default doesn’t include this prefix in its routing. This means that if you have a route defined as ``, Flask will only respond to requests without the prefix, i.e., ``.

Why is this a Problem?

This might not seem like a big deal, but it can lead to several issues, including:

• Broken links: If your application has links that point to other routes within the app, they will break if the prefix is not included.
• SEO issues: Search engines will index your routes without the prefix, leading to duplicate content and affecting your SEO.
• Inconsistent behavior: Depending on how your app is deployed, users might access your app with or without the prefix, leading to inconsistent behavior.

How to Ensure Flask Includes the Prefix

Now that we understand the problem, let’s move on to the solution. There are two ways to ensure Flask includes the prefix set by the Kubernetes Ingress controller:

Method 1: Using the `SCRIPT_NAME` Environment Variable

The first method involves setting the `SCRIPT_NAME` environment variable in your Flask application. This variable tells Flask what the prefix is, and it will include it in its routing.

To set the `SCRIPT_NAME` environment variable, you can add the following code to your Flask app:

from flask import Flask

app = Flask(__name__)

@app.before_request
def set_script_name():
    app.config['SCRIPT_NAME'] = os.environ.get('SCRIPT_NAME', '')

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

In the code above, we’re setting the `SCRIPT_NAME` configuration variable to the value of the `SCRIPT_NAME` environment variable. This variable is usually set by the Kubernetes Ingress controller.

Method 2: Using a Custom WSGI Middleware

The second method involves creating a custom WSGI middleware that sets the `SCRIPT_NAME` environment variable. This approach is useful if you’re using a WSGI server like Gunicorn.

To create a custom WSGI middleware, add the following code to a new file, e.g., `middleware.py`:

class PrefixMiddleware:
    def __init__(self, app, prefix()):
        self.app = app
        self.prefix = prefix

    def __call__(self, environ, start_response):
        environ['SCRIPT_NAME'] = self.prefix
        return self.app(environ, start_response)

In the code above, we’re creating a `PrefixMiddleware` class that takes an app and prefix as arguments. The `__call__` method sets the `SCRIPT_NAME` environment variable to the prefix and then calls the app.

To use this middleware, add the following code to your Flask app:

from flask import Flask
from middleware import PrefixMiddleware

app = Flask(__name__)

app.wsgi_app = PrefixMiddleware(app.wsgi_app, os.environ.get('SCRIPT_NAME', ''))

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

In the code above, we’re wrapping the Flask app with the `PrefixMiddleware` middleware, passing the `SCRIPT_NAME` environment variable as an argument.

Configuring Kubernetes Ingress

Now that we’ve set up our Flask app to include the prefix, let’s configure the Kubernetes Ingress controller to set the prefix.

Create a new file, e.g., `ingress.yaml`, with the following content:

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  name: flask-ingress
spec:
  rules:
  - host: example.com
    http:
      paths:
      - path: /api/v1
        backend:
          serviceName: flask-service
          servicePort: 80

In the code above, we’re defining an Ingress resource that sets the prefix to `/api/v1` for the `flask-service` service.

Apply the Ingress configuration to your Kubernetes cluster using the following command:

kubectl apply -f ingress.yaml

Verifying the Setup

Now that we’ve set up our Flask app and Kubernetes Ingress controller, let’s verify that the prefix is being included in our routes.

Start your Flask app and access it using a tool like `curl`:

curl http://example.com/api/v1/users

If everything is set up correctly, you should see the prefix included in the response.

Conclusion

In this article, we’ve covered two methods for ensuring Flask includes the prefix set by the Kubernetes Ingress controller. By following these steps, you can ensure that your Flask app is deployed correctly on Kubernetes and that the prefix is included in your routes.

Remember, whether you’re using the `SCRIPT_NAME` environment variable or a custom WSGI middleware, the key is to configure your Flask app to use the prefix set by the Ingress controller.

By following this guide, you’ll be well on your way to deploying scalable and secure Flask applications on Kubernetes!

Method	Description
Using `SCRIPT_NAME` Environment Variable	Sets the `SCRIPT_NAME` configuration variable to the value of the `SCRIPT_NAME` environment variable
Using Custom WSGI Middleware	Creates a custom WSGI middleware that sets the `SCRIPT_NAME` environment variable

Which method do you prefer? Let us know in the comments!

Frequently Asked Question

Get the lowdown on how to ensure Flask includes the prefix set by Kubernetes Ingress with these top 5 FAQs!