19 Background Tasks

title: Background Tasks in FastAPI REST APIs weight: 29 date: 2026-06-28 lastmod: 2026-06-28 description: Implement background tasks in FastAPI using BackgroundTasks for lightweight async operations after response delivery, and Celery for distributed task queues. tags: [api-development, fastapi]

FastAPI BackgroundTasks run lightweight post-response operations like email notifications and log cleanup, while Celery handles distributed, production-grade task queues for heavy processing with retry logic.

```python
from fastapi import FastAPI, BackgroundTasks

app = FastAPI()

def write_log(message: str):
    with open("log.txt", "a") as f:
        f.write(f"{message}\n")

def send_welcome_email(email: str, username: str):
    print(f"Sending welcome email to {email} for user {username}")

@app.post("/api/users", status_code=201)
def create_user(username: str, email: str, background_tasks: BackgroundTasks):
    background_tasks.add_task(send_welcome_email, email, username)
    background_tasks.add_task(write_log, f"User created: {username}")
    return {"message": "User created", "username": username}

What's Next

Now learn about file upload in Building REST APIs with FastAPI.