fastapi_otel.py

from typing import Awaitable, Callable
from fastapi import FastAPI, Request, Response
from fastapi.exceptions import HTTPException
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.propagate import inject
from opentelemetry.instrumentation.fastapi import FastAPIInstrumentor

trace.set_tracer_provider(TracerProvider())

app = FastAPI()

@app.get("/")
async def root():
    raise HTTPException(status_code=403)

@app.middleware("http")
async def inject_opentelemetry_response_headers(
    request: Request,
    call_next: Callable[[Request], Awaitable[Response]]
) -> Response:
    response: Response = await call_next(request)
    inject(response.headers)
    return response

FastAPIInstrumentor.instrument_app(app)

if __name__ == "__main__":
    from fastapi.testclient import TestClient
    t = TestClient(app)
    r = t.get("/")
    print(r.headers)