Python Flask Web application not able to deploy on Heroku using Waitress server

Question

I am trying to deploy my Flask application on Heroku PaaS Cloud Service. It, however, works on localhost with no errors. I am using git for version control and pushing to Heroku. Initially, as a web server, I used 'gunicorn' but later came to know it is useful for UNIX distributions. So I resorted my webserver to 'waitress'. I saw some of the posts and tried everything in the Procfile for hosting to Heroku. My Procfile reads like: web: waitress-serve --port=$PORT app:app. I also know that the first app in this line is the package and the second app is the name of the instance best to my knowledge. I even changed from app to myapp, website and I have all the packages including these mentioned are in my VS code editor. But my application is not getting deployed onto Heroku and it gives Application Error. Now when I check the logs using heroku logs --tail it gives me the following error as in the screenshot. Any help would be highly obliged. I am trying this for 23 hours. Heroku Logs

Answer 1

The Procfile looks correct but the problem could be that the file (app.py) and the variable (app) have the same name.

I suggest the following approach, in app.py

# define Flask app
def create_app():
  try:

    web_app = Flask(__name__)

    logging.info('Starting up..')

    return web_app

  except Exception as e:
    logging.exception(e)

# retrieve port
def get_port():
  return int(os.environ.get("PORT", 5000))

# start Flask app
if __name__ == '__main__':
  web_app = create_app()

  web_app.run(debug=False, port=get_port(), host='0.0.0.0')

The application can be launched from the Procfile with

web: waitress-serve --port=$PORT --call 'app:create_app'