fix: mount metrics to /metrics and its subpaths

api/chatbot/main.py

@@ -1,17 +1,19 @@
 """Main entrypoint for the app."""
 
+import re
 from contextlib import asynccontextmanager
 
 from fastapi import FastAPI, status
 from fastapi.encoders import jsonable_encoder
 from fastapi.requests import Request
-from fastapi.responses import JSONResponse, RedirectResponse
+from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
 from fastapi.templating import Jinja2Templates
 from langgraph.checkpoint.postgres.aio import AsyncPostgresSaver
 from loguru import logger
 from prometheus_client import make_asgi_app
 from sqlalchemy.exc import NoResultFound
+from starlette.routing import Mount
 
 from chatbot.config import settings
 from chatbot.dependencies import EmailHeaderDep, UserIdHeaderDep, UsernameHeaderDep
@@ -47,17 +49,11 @@ async def lifespan(app: FastAPI):
 )
 
 # Add prometheus asgi middleware to route /metrics requests
-metrics_app = make_asgi_app()
-app.mount("/metrics/", metrics_app)
-
-
-# NOTE: Even I mounted it to `/metrics`, I must append the trailing slash to access the metrics. i.e. `/metrics/`
-# I think it's a bug in fastapi.
-# My current solution is to add a redirect endpoint for this specific request.
-@app.get("/metrics")
-async def redirect_to_metrics_with_slash():
-    return RedirectResponse(url="/metrics/")
-
+metrics_route = Mount("/metrics", make_asgi_app())
+# @See https://github.com/prometheus/client_python/issues/1016#issuecomment-2088243791
+# @See https://github.com/vllm-project/vllm/pull/4511#issuecomment-2088375895
+metrics_route.path_regex = re.compile("^/metrics(?P<path>.*)$")
+app.routes.append(metrics_route)
 
 app.include_router(chat_router)
 app.include_router(conversation_router)