Chapter 34: Background Tasks and Services

ASP.NET Core has hosted services and background services. FastAPI has in-process background tasks, but they are only suitable for small, non-critical follow-up work.

Use in-process background tasks for:

• Sending a low-risk notification after a response.
• Writing an audit event when losing it is acceptable.
• Small cleanup work.

Use a real worker queue for:

• Email delivery that must retry.
• Image processing.
• Long imports and exports.
• Scheduled jobs.
• Work that must survive app restarts.

Python worker choices:

• Celery: mature, widely used, heavier.
• Dramatiq: simpler queue workers.
• ARQ: asyncio Redis queue.
• RQ: straightforward Redis jobs.
• APScheduler: scheduling inside a process, not a durable queue by itself.

RecipeVault background work:

• Import recipes from a URL.
• Export a user's recipes to CSV.
• Generate search indexes.
• Send account emails.

Keep background job code in application services so the web request and worker can call the same use case safely.