Flask-socketio: Push notifications from a background process on the server

[ghost]

I am not sure of the best way to create a push notification from a background service on my server to notify the client. This background service (run from within a flask_script) runs between 08:00 and 16:30 Monday to Friday. This service polls an API and does some machine learning to predict future stock values. At the moment, I am slightly confused as to how I would notify the running app that this process has completed and that a socket needs to emit a message to the client. I have the current implementation of my repository under flask_react_app on the branch flask_socketio_sql_alchemy_intergration.

[miguelgrinberg]

Emitting events from an external process is covered in the documentation: https://flask-socketio.readthedocs.io/en/latest/#emitting-from-an-external-process.

If you want an actual example, my Flack example emits from a Celery worker. The same idea can be applied to other types of processes.

[ghost]

Thanks for the reply. I will look into the way your Flack example uses the Celery worker. Hopefully I should be able to apply this idea to my own process. 👍

[ghost]

I have implemented a celery background task which emits, however, my client side appear to not receive any sort of update.

Here is what I currently have. I believe the problem is within the flask_react_app where I instantiate the application and specify the message queue.

I am using gunicorn with eventlet to serve the app as seen in the Procfile.

[miguelgrinberg]

Are you running a message queue?

[ghost]

Thanks for your quick reply! I believe so. I am running the redis-server. If that's what you mean by message queue?

[miguelgrinberg]

What I mean is that I don't see anywhere in your code that you have configured the queue. Did you see the docs on how to run an external process emitter?

[ghost]

I'll have another look. Thanks for your help btw.

[ghost]

Isn't this line socketio = SocketIO(message_queue=os.environ["CELERY_BROKER_URL"]) setting the message queue? Within the flask_react_app init?

[miguelgrinberg]

I suggest you look at the docs, plus the Flack application I referenced earlier. You need to configure the message queue on the server and the external process.

[ghost]

Okay. I'll keep at it. If I run into anymore problems I'll post within this issue. Again, thanks for the help.

[ghost]

I think I'm getting there. I have recently committed some new changes which are more inline with the way the flack application operates. I have attached the message queue in both external process and the server (I think). I am now getting an error within the celery worker as follows:

ImportError: import_string() failed for 'config.DevelopmentConfig'. Possible reasons are:

- missing __init__.py in a package;
- package or module path not included in sys.path;
- duplicated package or module name taking precedence in sys.path;
- missing module, class, function or variable;

Debugged import:

- 'config' not found.

Original exception:

ImportStringError: import_string() failed for 'config'. Possible reasons are:

- missing __init__.py in a package;
- package or module path not included in sys.path;
- duplicated package or module name taking precedence in sys.path;
- missing module, class, function or variable;

[miguelgrinberg]

That seems unrelated to the change that you made. Sounds like an import for config is failing. Not sure how I can help with this, you have to locate the import and figure out why it is incorrect.

[ghost]

Thanks for all your help! I have now been able to emit through an external process!