[FIXED] Gunicorn3 goes to the development server

Issue

When I open a server with gunicorn for my flask app, it automatically opens the development server of flask, without giving me any errors:

$ gunicorn3 --workers=1 main:app
\[2023-10-16 19:46:13 +0000\] \[1061\] \[INFO\] Starting gunicorn 20.1.0
\[2023-10-16 19:46:13 +0000\] \[1061\] \[INFO\] Listening at: http://127.0.0.1:8000 (1061)
\[2023-10-16 19:46:13 +0000\] \[1061\] \[INFO\] Using worker: sync
\[2023-10-16 19:46:13 +0000\] \[1062\] \[INFO\] Booting worker with pid: 1062

* Serving Flask app 'app'
* Debug mode: off
  2023-10-16 19:46:14,209:INFO - WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
* Running on http://127.0.0.1:5000
  2023-10-16 19:46:14,209:INFO - Press CTRL+C to quit

I already have other servers with gunicorn and I don't understand this behavior, does someone know?

I've changed the port and the host, but the outcome is the same, also with the debug mode and the number of workers of gunicorn3.

Solution

If you have the following lines in your main application script then it will cause Flask's development server to start

if __name__ == '__main__':
    app.run()

• You could comment out the above part
• Make sure that you don't have any environment variables like FLASK_ENV=development or FLASK_APP=app.py
• Confirm that main:app correctly points to your Flask application object

Answered By - Yuri R