How to add metrics

[pawamoy]

Hello! Thanks for the projet 🙂

I read the README and I'm left wondering how I can add metrics to the already defined ones. Is this even possible yet? For example, I'd like to add the average transfered data size per request/response. How would I add this into the instrumentator?

[trallnag]

Do you want the transfered data metric just for a few specific endpoints or all endpoints transparently?

Option 1: Instrument the specific endpoints manually by directly using the Prometheus library.

Option 2: Not supported. I could put it on my bucket list. Though I'm not sure if I would hardcode the new metrics or do something like @rycus86 has done in his package for instrumenting Flask apps https://github.com/rycus86/prometheus_flask_exporter.

And thanks

[pawamoy]

Thanks for the quick answer!

Do you want the transfered data metric just for a few specific endpoints or all endpoints transparently?

Depends! It was just an example 🙂 Could be both.

Oh yes, it seems prometheus_flask_exporter allows to do what I'm looking for.

So I would say: don't hardcode it! Instead, provide a way for users to add their own custom, exported metrics.

[trallnag]

@pawamoy you can now select from a few already existing instrumentations or add your own. Check the updated README.md for more info.

Recording size of requests / responses:

instrumentator.add(
    metrics.request_size(
        should_include_handler=False,
        should_include_method=False,
        should_include_status=False,
    )
).add(
    metrics.response_size(
        should_include_handler=False,
        should_include_method=False,
        should_include_status=False,
    )
)

Or creating your own:

def http_requested_languages_total() -> Callable[[Info], None]:
    METRIC = Counter(
        "http_requested_languages_total", 
        "Number of times a certain language has been requested.", 
        labelnames=("langs",)
    )

    def instrumentation(info: Info) -> None:
        langs = set()
        lang_str = info.request.headers["Accept-Language"]
        for element in lang_str.split(",")
            element = element.split(";")[0].strip().lower()
            langs.add(element)
        for language in langs:
            METRIC.labels(language).inc()

    return instrumentation

instrumentator.add(http_requested_languages_total())