Flask-SocketIO Client: Event Handlers Not Logging or Debugging — Even With app.app_context()

[mahdipython614]

Hi Miguel,

Thanks for your work on Flask-SocketIO — it’s been really helpful.

I’m using socketio.Client inside a Celery worker, where Flask is initialized only to support SQLAlchemy models. There are no Flask routes or HTTP requests — this is a pure client-side use case. All event handlers are triggered by incoming Socket.IO messages handled inside Celery.

Here’s the issue I’m facing:

Inside these event handlers, no logging appears, and breakpoints are never hit, even in debug mode.

I’ve tried wrapping the handlers in app.app_context(), but that makes no difference — it's as if Flask isn't running at all.

Since Celery executes these handlers, I suspect Flask's app context is entirely disconnected from the runtime environment, so app.app_context() has no visible effect.

So my question is:

In a Flask + Celery setup where Socket.IO events are handled in workers (without any HTTP context), how can I ensure that logging, debugging, and SQLAlchemy access work properly inside these event functions?

Any suggestions or best practices would be greatly appreciated.

Thanks again for your time,

[miguelgrinberg]

Unfortunately you are not providing sufficient details, but I think you must be making some incorrect assumptions.

Inside these event handlers, no logging appears

Are the handlers running? What logging do you expect to see? Are you writing your own logging inside these handlers?

and breakpoints are never hit

Strong indication that the handlers aren't running.

even in debug mode.

This does not really mean anything in the Celery worker. If you refer to Flask's debug mode, that is a server feature. The Celery worker isn't running a Flask server.

it's as if Flask isn't running at all

This is actually correct. Flask is a web server, it is not supposed to run in your Celery worker. The only reason you need a Flask app instance in the worker is to have access to the configuration, which I assume is needed by some of the Flask extensions you are using.

In a Flask + Celery setup where Socket.IO events are handled in workers (without any HTTP context), how can I ensure that logging, debugging, and SQLAlchemy access work properly inside these event functions?

There is no such thing as "Flask + Celery". In the Celery worker you can use Flask extensions if you need them, but Flask itself does not do anything. And with respect to Socket.IO, I believe you said this is a Socket.IO client, correct? The Socket.IO client has absolutely no knowledge of Flask, it does not need nor use Flask for anything.