Serving dynamic files on heroku?

Question

I have a flask app that has two threads. One modifies flask templates to keep them up to date from scraped info, and the other is the flask server that takes incoming route requests.

from flask import Flask, render_template
import threading
import RunArbIfDown
app = Flask(__name__, static_url_path='')


@app.route('/')
def index():
    return render_template('index.html')

if __name__ == "__main__":
    threading.Thread(target=app.run).start()
    threading.Thread(target=RunArbIfDown.start).start() # this line continuously updates index.html (every 60s)

When I check the app, index.html is never updated even though there seem to be no errors. Are we allowed to modify files on the heroku dyno? Are there any good solutions for this?

Klaus D. · Accepted Answer · 2020-09-13T09:16:47.190

1

Running threads in a WSGI environment might yield unexpected results. The WSGI server usually manages threads and can create and kill them at any time.

Also you have protected your threading code with a __name__ condition. The code will execute if the file is started directly. A WSGI server will not do that. It will import the file and the the condition will not be met.

A typical way to run recurring tasks in Flask is to use a custom command via cron. It is run as a separate process.

edited Sep 13 '20 at 09:16

answered Sep 03 '20 at 03:19

Klaus D.

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Thanks for the insight @Klaus D. Would you be able to share a way of doing it with `cron` and without a `__name__ ` condition? – Jesse Reza Khorasanee Sep 03 '20 at 03:33
I should have mentioned in my question that this setup works fine locally, just not on heroku. – Jesse Reza Khorasanee Sep 03 '20 at 03:34
I've switched this question to a much more reproducible one at https://stackoverflow.com/questions/63749430/threading-not-working-with-flask-on-heroku – Jesse Reza Khorasanee Sep 05 '20 at 00:41

Serving dynamic files on heroku?

1 Answers1