Test test_expose_defaults fails due to NameError after updating

[trallnag]

Pull request #153 introduced new parameter registry to set Prometheus client registry. It also added two tests to cover this enhancement.

After running poetry update on commit 8cec83b the test_expose_defaults started to fail.

info = <prometheus_fastapi_instrumentator.metrics.Info object at 0x7f232b7433d0>

    def instrumentation(info: Info) -> None:
>       TOTAL.labels(info.method, info.modified_status, info.modified_handler).inc()
E       NameError: free variable 'TOTAL' referenced before assignment in enclosing scope

src/prometheus_fastapi_instrumentator/metrics.py:628: NameError

Before that it worked fine. It tried to debug it. The Prometheus client lib is complaining about duplicate metrics as excepted.

Duplicated timeseries in CollectorRegistry: {'http_requests_total', 'http_requests_created', 'http_requests'}

Problems start when updating starlette and fastapi

  • Updating starlette (0.22.0 -> 0.25.0)
  • Updating fastapi (0.88.0 -> 0.92.0)

[trallnag]

Hey @tiangolo, any idea what might have changed with the update that results in the test suddenly failing?

The hotfix seems to work (see PR) but would still be interesting to know

[frankie567]

Hey there 👋

Came across this and I thought I would put my two cents in. I think this problem was introduced because since Starlette 0.24.0, the middleware stack is built only once when app starts (and not each time add_middleware is called like before). Here is the relevant PR: encode/starlette#2017

IMHO, the fact that test_expose_defaults was passing was an happy consequence of side effects produced by the rebuild of the middleware stack. It shouldn't have passed like this, with the risk of having local variables undefined.

[dhodun]

This latest PR 220 fixed the issue in our environment. Looking forward to the PyPI update.
https://github.com/trallnag/prometheus-fastapi-instrumentator/pull/220/files

Was seeing it on an older version of starlette though:

starlette==0.20.4
fastapi==0.85.1
prometheus-fastapi-instrumentator==5.10.0