Textfile Collector write_to_textfile function overwriting metric with same name but different labels

[Daniel Lacher]

Greetings Prometheus users,

I have a function that is called a few times within a loop, and my idea was that the function would populate the .prom file by adding a new line every time, with the same metric name but with a different label. For example:

sv_api_response{method="getUserByID"} 1

sv_api_response{method="getUserByName"} 1

Etc. (1 when the API sends a 200 response, 0 otherwise)

But that doesn't happen. When the loop ends, I have only one line in the file, with the last written metric. Each time a new metric is written, it overwrites the previous one. My function is as follows:

from prometheus_client import CollectorRegistry, Gauge, write_to_textfile

...

def write_metric(method, expectation, response, region):

    registry = CollectorRegistry()

    gauge = Gauge('sv_api_response', '1 if API is up', ['method'], registry=registry)

    if response is not None:

        if response.status_code == expectation:

            gauge.labels(method).set(1)

        else:

            gauge.labels(method).set(0)

    else:

        gauge.labels(method).set(0)

    write_to_textfile('/opt/node_exporter/textfile_collector/sv.prom', registry)

Is there a way to make it preserve the metrics that it adds to the file and simply append the new ones?

Thank you.

Regards,

Daniel