OpenMetrics ignore_metrics documentation mismatch with behavior

[ottaviohartman]

#5759 added these examples to the openmetrics check conf.yaml:

    # ignore_metrics:
    #  - <IGNORED_METRIC_NAME>
    #  - <PREFIX_*>
    #  - <*_SUFFIX>
    #  - <PREFIX_*_SUFFIX>
    #  - <*_SUBSTRING_*>

However, the implementation uses fnmatch.translate (code here), which does not exactly work like the documentation says.

For example, the ignore_metric PREFIX_* would match both:

• PREFIX_HELLO
• THIS_IS_A_PREFIX_TOO

We came across this problem when trying to exclude high cardinality go_* metrics, while including argo_* metrics.

Steps to reproduce the issue:

1. Set ignore_metrics in the openmetrics check to _* and any metrics with _ in them (not just those that start with _) will be ignored.

Describe the results you expected:

We expected the documentation to be the expected behavior.

I suppose either the documentation should be fixed or the implementation.

[ottaviohartman]

cc @ahmed-mez for visibility

[ahmed-mez]

Hey @omh1280 thanks for opening this issue, and sorry for the trouble!

Opened #9729 to address this. Thanks!