Serve static files from a CDN rather than Flask in production

There's no need to change how you link to static files, you can still use url_for('static', filename='myfile.txt'). Replace the default static view with one that redirects to the CDN if it is configured.

from urllib.parse import urljoin
# or for python 2: from urlparse import urljoin
from flask import redirect

@app.endpoint('static')
def static(filename):
    static_url = app.config.get('STATIC_URL')

    if static_url:
        return redirect(urljoin(static_url, filename))

    return app.send_static_file(filename)

Whether you're on a dev machine or production, set the STATIC_URL config value to the CDN and requests for static files will be redirected there.

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Redirects are relatively cheap, and are remembered by browsers. If you get to the point where performance is meaningfully affected by them, you can write a function that links directly when using the CDN.

@app.template_global()
def static_url(filename):
    static_url = app.config.get('STATIC_URL')

    if static_url:
        return urljoin(static_url, filename)

    return url_for('static', filename=filename)

The template_global decorator makes the function available in all templates. Use it instead of url_for when you need urls for static files.

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There may be a Flask extension that does this for you already. For example, Flask-S3 provides a url_for that serves static files from AWS S3.

This flask cdn integration guide may be worth taking a read through. Basically you can install the Flask-CDN extension and define your CDN URL within your app.py file like so:

from flask import Flask
from flask.ext.cdn import CDN

app = Flask(__name__)
app.config['CDN_DOMAIN'] = 'cdn.yourdomain.com'
CDN(app)