Instrumentator appears to be broken with the latest FastAPI

[Fohlen]

When I bootstrap, a simple application with FastAPI >= 0.70.0 and add the instrumentator according to the documentation, it'll throw the following error:

Traceback (most recent call last):
  File "/Users/fohlen/.pyenv/versions/3.9.7/lib/python3.9/multiprocessing/process.py", line 315, in _bootstrap
    self.run()
  File "/Users/fohlen/.pyenv/versions/3.9.7/lib/python3.9/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/uvicorn/subprocess.py", line 76, in subprocess_started
    target(sockets=sockets)
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/uvicorn/server.py", line 68, in run
    return asyncio.run(self.serve(sockets=sockets))
  File "/Users/fohlen/.pyenv/versions/3.9.7/lib/python3.9/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "uvloop/loop.pyx", line 1501, in uvloop.loop.Loop.run_until_complete
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/uvicorn/server.py", line 76, in serve
    config.load()
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/uvicorn/config.py", line 448, in load
    self.loaded_app = import_from_string(self.app)
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/uvicorn/importer.py", line 21, in import_from_string
    module = importlib.import_module(module_str)
  File "/Users/fohlen/.pyenv/versions/3.9.7/lib/python3.9/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1030, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1007, in _find_and_load
  File "<frozen importlib._bootstrap>", line 986, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 680, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "/Users/fohlen/PyCharmProjects/api-data/sanic-api/fast_api.py", line 101, in <module>
    Instrumentator().instrument(app).expose(app, tags=["metrics"])
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/prometheus_fastapi_instrumentator/instrumentation.py", line 127, in instrument
    self.instrumentations.append(metrics.default())
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/prometheus_fastapi_instrumentator/metrics.py", line 563, in default
    TOTAL = Counter(
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/prometheus_client/metrics.py", line 136, in __init__
    registry.register(self)
  File "/Users/fohlen/.pyenv/versions/sanic-api/lib/python3.9/site-packages/prometheus_client/registry.py", line 29, in register
    raise ValueError(
ValueError: Duplicated timeseries in CollectorRegistry: {'http_requests_total', 'http_requests', 'http_requests_created'}

I suspect this is because the async library changed to anyio, but I'm not too deep into the code to submit a fix.

[Fohlen]

How this is fixed is by delaying the initialization of the app.

If you do the following:

@app.on_event("startup")
async def startup_event():
    Instrumentator().instrument(app).expose(app)

It'll work just fine. This is because Prometheus expects a fully initialized ASGI client, where uvicorn now delays execution in newer versions. Closing.