Flask Heroku 上的应用程序在部署后出现应用程序错误

Question

I'm trying to run a Flask app with Gunicorn on Heroku.

This is my Procfile :

web: gunicorn main: app

I have a file called main.py . Here is some of the code at the top:

from flask import Flask, redirect, url_for, render_template, request, session, flash
from datetime import timedelta, datetime
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.secret_key = "{Secret Key}"
app.permanent_session_lifetime = timedelta(minutes=10)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.sqlite3'
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False

db = SQLAlchemy(app)

....

if __name__ == "__main__":
    db.create_all()
    app.run(debug=True)

My requirements.txt :

click==7.1.2
Flask==1.1.2
Flask-SQLAlchemy==2.4.4
gunicorn==20.0.4
itsdangerous==1.1.0
Jinja2==2.11.2
MarkupSafe==1.1.1
SQLAlchemy==1.3.22
Werkzeug==1.0.1

I'm getting this in my logs:

2020-12-31T00:00:05.879585+00:00 app[web.1]: Failed to parse '' as an attribute name or function call.
2020-12-31T00:00:05.880396+00:00 app[web.1]: [2020-12-31 00:00:05 +0000] [11] [INFO] Worker exiting (pid: 11)
2020-12-31T00:00:05.887417+00:00 app[web.1]: Failed to parse '' as an attribute name or function call.
2020-12-31T00:00:05.888296+00:00 app[web.1]: [2020-12-31 00:00:05 +0000] [10] [INFO] Worker exiting (pid: 10)
2020-12-31T00:00:06.139402+00:00 app[web.1]: [2020-12-31 00:00:06 +0000] [4] [INFO] Shutting down: Master
2020-12-31T00:00:06.139670+00:00 app[web.1]: [2020-12-31 00:00:06 +0000] [4] [INFO] Reason: App failed to load.
2020-12-31T00:00:06.291109+00:00 heroku[web.1]: Process exited with status 4
2020-12-31T00:00:06.360098+00:00 heroku[web.1]: State changed from up to crashed
2020-12-31T00:00:12.000891+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" [some extra stuff]
2020-12-31T00:00:12.118356+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" [some extra stuff]

The Procfile looks to be right from what I've read online but otherwise I don't see anything wrong with this. Does anyone know what's going on with this?

Answer 1

Remove the space between main and app :

web: gunicorn main:app

Gunicorn wants a [WSGI_APP]

Where WSGI_APP is of the pattern $(MODULE_NAME):$(VARIABLE_NAME) . The module name can be a full dotted path. The variable name refers to a WSGI callable that should be found in the specified module.

With the space, main: and app are read as separate arguments and Gunicorn receives an empty string as its VARIABLE_NAME .