How to manage session state with FastAPI when using background tasks?
I can't seem to get I'm working on a FastAPI application (version 0.68.0) that needs to handle session state while executing background tasks... I want to store some user-specific data in the session but have run into issues where the session data appears to be lost after the background task is executed. Here's a simplified version of my code: ```python from fastapi import FastAPI, BackgroundTasks, Depends, Cookie from fastapi.responses import HTMLResponse from fastapi.middleware.cors import CORSMiddleware app = FastAPI() app.add_middleware(CORSMiddleware, allow_origins=['*'], allow_credentials=True, allow_methods=['*'], allow_headers=['*']) def get_session_id(session_id: str = Cookie(None)): return session_id @app.get('/', response_class=HTMLResponse) async def main_page(session_id: str = Depends(get_session_id)): return f'<h1>Your session ID is: {session_id}</h1>' @app.post('/start_task/') async def start_background_task(session_id: str = Depends(get_session_id), background_tasks: BackgroundTasks = BackgroundTasks()): background_tasks.add_task(perform_task, session_id) return {'message': 'Task started'} async def perform_task(session_id: str): # Simulate a long-running task await asyncio.sleep(5) print(f'Task completed with session ID: {session_id}') ``` When I run this code and trigger the `/start_task/` endpoint, the task completes successfully, but the `session_id` seems to be `None` in the `perform_task` function, which causes issues when I try to use that ID for database interactions. I've confirmed that the session cookie is being sent correctly in the request. I have tried using global variables to store session data or using FastAPI's dependency injection to pass the session ID to the background task, but nothing seems to work. I'm also aware that background tasks run in a separate context than the original request, which may be causing the data loss. Is there a proper way to retain session state across background tasks in FastAPI? Any insights on best practices would be greatly appreciated! For context: I'm using Python on Linux. Am I missing something obvious? I'm working with Python in a Docker container on Debian. What would be the recommended way to handle this? I'm working in a CentOS environment. Any ideas what could be causing this?