Running Heroku background tasks with only 1 web dyno and 0 worker dynos

Question

I have a Python Flask app on Heroku that serves web pages but also allows certain tasks to be launched which I believe would be best structured as background tasks. As such

Answer 1

I am currently running both my web and backend scheduler in Heroku using only 1 dyno.

Idea is to provide one main python script for Heroku to start in 1 dyno. This script is used to start both the web server process(es) and the customer scheduler process(es). You can then define your jobs and add them to the custom scheduler.

APScheduler is used in my case.

This is what I did:

in Procfile:

 web: python run_app.py    #the main startup script

in the run_app.py:

# All the required imports
from apscheduler.executors.pool import ThreadPoolExecutor, ProcessPoolExecutor
from apscheduler.triggers.cron import CronTrigger
from run_housekeeping import run_housekeeping
from apscheduler.schedulers.background import BackgroundScheduler
import os

def run_web_script():
    # start the gunicorn server with custom configuration
    # You can also using app.run() if you want to use the flask built-in server -- be careful about the port
    os.system('gunicorn -c gunicorn.conf.py web.jobboard:app --debug')  

def start_scheduler():

     # define a background schedule 
     # Attention: you cannot use a blocking scheduler here as that will block the script from proceeding.
     scheduler = BackgroundScheduler()

     # define your job trigger
     hourse_keeping_trigger = CronTrigger(hour='12', minute='30')

     # add your job
     scheduler.add_job(func=run_housekeeping, trigger=hourse_keeping_trigger)

     # start the scheduler
     scheduler.start()


def run():
    start_scheduler()
    run_web_script()

if __name__ == '__main__':
    run()

I am also using 4 Worker processes for serving the web from Gunicorn -- which runs perfectly fine.

In gunicorn.conf.py:

loglevel = 'info'
errorlog = '-'
accesslog = '-'
workers = 4

You may want to checkout this project as an example: Zjobs@Github