# Problem with FastAPI's Background Tasks

**URL:** <https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773>\
**Category:** Ray Serve\
**Created:** [May 24, 2023, 2:03pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773 "2023-05-24T14:03:04Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Alpe6825](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/alpe6825/32/3214_2.png) [@Alpe6825](https://discuss.ray.io/u/Alpe6825)\
**Post date:** [May 24, 2023, 2:03pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/1 "2023-05-24T14:03:04Z")

</div>

I would like to make a request, which starts a process and returns before waiting until the started process is finished. With FastAPI it’s possible to archive this with background tasks:

```auto
app = FastAPI()

def long_process(id: str):
    time.sleep(10)
    print(f"{id} has been processed.")

@app.get("/")
async def test_bgtask(background_tasks: BackgroundTasks):
    background_tasks.add_task(long_process, "1234")
    return {"response before finish processing"}

if __name__ == " __main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

```

If I combine FastAPI with Ray Serve then it didn’t worked. Here the response waits for the background task:

```auto
app = FastAPI()

def long_process(id: str):
    time.sleep(10)
    print(f"{id} has been processed.")

@app.get("/")
async def test_bgtask(background_tasks: BackgroundTasks):
    background_tasks.add_task(long_process, "1234")
    return {"response before finish processing"}

@serve.deployment(route_prefix="/")
@serve.ingress(app)
class FastAPIWrapper:
    pass

serve.run(FastAPIWrapper.bind())
print("send request")
resp = requests.get("http://localhost:8000/")
print(resp)

```

Any idea how I can archive it?

---

<div class="post-metadata">

**Author:** ![eoakes](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/eoakes/32/7825_2.png) [@eoakes](https://discuss.ray.io/u/eoakes)\
**Post date:** [May 24, 2023, 4:18pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/2 "2023-05-24T16:18:05Z")

</div>

@Alpe6825 what was the behavior you observed when using the Ray Serve version?

---

<div class="post-metadata">

**Author:** ![Alpe6825](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/alpe6825/32/3214_2.png) [@Alpe6825](https://discuss.ray.io/u/Alpe6825)\
**Post date:** [May 24, 2023, 4:52pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/3 "2023-05-24T16:52:58Z")

</div>

`resp` will be returned after 10s.

---

<div class="post-metadata">

**Author:** ![eoakes](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/eoakes/32/7825_2.png) [@eoakes](https://discuss.ray.io/u/eoakes)\
**Post date:** [May 24, 2023, 4:56pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/4 "2023-05-24T16:56:47Z")

</div>

I see, and what if you try:

```python
async def long_process(id: str):
    await asyncio.sleep(10)
    print(f"{id} has been processed.")

```

?

(maybe it’s related to the event loop blocking)

---

<div class="post-metadata">

**Author:** ![Alpe6825](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/alpe6825/32/3214_2.png) [@Alpe6825](https://discuss.ray.io/u/Alpe6825)\
**Post date:** [May 30, 2023, 11:04am UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/5 "2023-05-30T11:04:35Z")

</div>

nothing changed. `resp` will be returned after 10s again.

But I found a little workaround when I don’t use ray serve but FastAPI and RayCore. Instead of a FastAPI Background task I use a ray task like this

```plaintext
@ray.remote
def long_process(id: str):
    time.sleep(10)
    print(f"{id} has been processed.")

@app.get("/")
async def test_bgtask():
    long_process.remote("1234")
    return {"response before finish processing"}

```

I found this workaround [here](https://discuss.ray.io/t/fastapi-ray-core-vs-fastapi-ray-serve/1214).

@eoakes Do you think this workaround has any disadvantages in comparison to ray serve?

---

<div class="post-metadata">

**Author:** ![ValerioL29](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ray.io/valeriol29/32/7708_2.png) [@ValerioL29](https://discuss.ray.io/u/ValerioL29)\
**Post date:** [February 24, 2025, 2:05pm UTC](https://discuss.ray.io/t/problem-with-fastapis-background-tasks/10773/6 "2025-02-24T14:05:36Z")

</div>

Hey guys! I tried to add background tasks to my Ray Serve endpoints, but I followed the [official docs](https://fastapi.tiangolo.com/tutorial/background-tasks/) of FastAPI and found `BackgroundTasks` from `FastAPI` cannot achieve my goal as the `add_tasks` method is not an async function.

After a bit of workarounds in this topic, the correct answer is to directly use the `BackgroundTask` or `BackgroundTasks` from the `starlette.background` module. Generally, the boilerplate will be like -

```python
import uuid

import ray
from ray.serve.handle import DeploymentHandle
from starlette.background import BackgroundTask
from starlette.responses import JSONResponse

app = FastAPI()

@serve.deployment
@serve.ingress(app)
class YourAppIngress:
    def __init__ (self, deployment_handler: DeploymentHandle):
        self.handler = deployment_handler
    
    @app.post("/schedule")
    def schedule(self, path_or_query_or_body_params_as_usual: str):
        try:
            # Optional session_id, or task_id, etc.
            session_id = str(uuid.uuid1())
            your_background_task = BackgroundTask(
                self.handler.handle_long_running_request.remote,
                session_id,
                path_or_query_or_body_params_as_usual,
                other_params_that_you_need_to_pass_to_your_task_function
            )
        except Exception as e:
            raise HTTPException(status_code=404, detail=f"Failed to schedule due to: {e}") from None
        return JSONResponse(
            content={
                "session_id": session_id,
                "message": "Successfully scheduled.",
            },
            background= your_background_task,
        )

```

🙂 Hope it would help those who are struggling to find a solution.