Zombie SharedDataMiddleware on Python Heroku

Question

I'm setting up a Flask app on Heroku. Everything is working fine until I added static files. I'm using this:

from werkzeug import SharedDataMiddleware
app = Flask(__name__)
app.wsgi_app = SharedDataMiddleware(app.wsgi_app, {'/static': os.path.join(os.path.dirname(__file__), 'static') })

The first time I deploy the app, the appropriate files in the ./static will be available at herokuapp.com/static. But after that initial deploy, the files never change on Heroku. If I change the last line to:

app.wsgi_app = SharedDataMiddleware(app.wsgi_app, {'/assets': os.path.join(os.path.dirname(__file__), 'static') })

a new URL for the static files, herokuapp.com/assets, then I can see the updated files.

It seems like a mirror of the files gets stuck in the system. I've changed it four times and can access all of the URLs still.

Answer 1

SharedDataMiddleware defaults to sending Cache-Control and Expires HTTP headers, which means that your web browser may not even send a request to the server and just use the old files from cache. Try disabling the cache:

app.wsgi_app = SharedDataMiddleware(
    app.wsgi_app,
    {'/static': os.path.join(os.path.dirname(__file__), 'static')},
    cache=False)

Flask does the same with static files. To disable it there:

app.config['SEND_FILE_MAX_AGE_DEFAULT'] = None