Exclude background tasks from request duration in ASGI middleware #1684
Description
Is your feature request related to a problem?
The duration of a request span in FastAPI includes the duration of evaluating background tasks. There is no span whose duration represents the time bewteen receiving a request and sending the response. An example:
import asyncio
from typing import TypedDict
from fastapi import BackgroundTasks, Depends, FastAPI
from opentelemetry import trace
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor, ConsoleSpanExporter
app = FastAPI()
exporter = ConsoleSpanExporter()
provider = TracerProvider()
processor = BatchSpanProcessor(exporter)
provider.add_span_processor(processor)
trace.set_tracer_provider(provider)
FastAPIInstrumentor.instrument_app(app)
def get_context(
background_tasks: BackgroundTasks,
):
return Context(background_tasks=background_tasks)
async def some_background_task():
await asyncio.sleep(10)
class Context(TypedDict):
background_tasks: BackgroundTasks
@app.get("/")
async def main(context=Depends(get_context)):
print(context.keys())
context["background_tasks"].add_task(some_background_task)
return NoneDescribe the solution you'd like
Either end the server span after we have sent the response (this is how dd-trace solve it in DataDog/dd-trace-py#3799)
OR create a new span that stops after the response has been sent.
Additional context
This is important to calculation latency metrics using the FastAPI instrumentation