This browser is no longer supported.
Upgrade to Microsoft Edge to take advantage of the latest features, security updates, and technical support.
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(38.4, 51%, 13%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EM%3C/text%3E%3C/svg%3E)
99% of you our fastapi requests are in the <500ms response time range. Yet we regularly see single requests that time out with no real pattern. From application insights we do not get a stacktrace or any info on what went wrong within our code. The "work" and logic the backend has to go through for generating the response is minimal, so we can't figure out why it fails sometimes.
How can we find the root cause of the timeouts?
Here is the information we see in Application insights:
EXCEPTION
Microsoft.Azure.WebJobs.Host.FunctionTimeoutException
Exception Properties
Show all
Event time 9/7/2022, 3:17:14.757 PM (Local time)
Message Timeout value of 00:05:00 was exceeded by function: Functions.app
Exception type Microsoft.Azure.WebJobs.Host.FunctionTimeoutException
Failed method Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor+
![](data:image/svg+xml, %3Csvg xmlns='http://www.w3.org/2000/svg' height='64' class='font-weight-bold' style='font: 600 30.11764705882353px "SegoeUI", Arial' width='64'%3E%3Ccircle fill='hsl(188.79999999999998, 79%, 28%)' cx='32' cy='32' r='32' /%3E%3Ctext x='50%25' y='55%25' dominant-baseline='middle' text-anchor='middle' fill='%23FFF' %3EMD%3C/text%3E%3C/svg%3E)
Could you please show the code on the entry function? How you are starting the fastapi?
here is a shortened version of our entry point main.py:
import logging
import logging.config
import azure.functions as func
import nest_asyncio
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware
from .routes import router
from .settings import auth_settings, azure_scheme, fastapi_settings, log_config
logging.config.dictConfig(log_config)
fastapi_app = FastAPI(**fastapi_settings.__dict__)
fastapi_app.include_router(router)
@fastapi_app.on_event("startup")
async def startup() -> None:
await azure_scheme.openid_config.load_config()
fastapi_app.add_middleware(
CORSMiddleware,
allow_origins=[str(origin) for origin in auth_settings.BACKEND_CORS_ORIGINS],
allow_credentials=True,
allow_methods=["*"],
allow_headers=["*"],
)
nest_asyncio.apply()
async def main(req: func.HttpRequest, context: func.Context) -> func.HttpResponse:
"""Run in azure environment"""
startup() # startup event does not get triggered by azure
return func.AsgiMiddleware(fastapi_app).handle(req, context)
This may or may not help but I would start with Application Map. This should help provide insight into the request(s) that's timing out and any associated dependencies with the said request. Storage accounts, databases, custom DNS, even App Insights itself could be issues that's causing your timeout issue.
The application map shows the slowest request of the past 7 days as 350ms, which does not match with what I see when I look at the slowest transactions. We have requests slower than a minute.