_created metrics are not created in multi-process mode about prometheus-fastapi-instrumentator

[trallnag]

Hi @zdets, bad news, this is actually not supported by the official Prometheus client library that is used by this package. In previous versions of this package the /metrics endpoint in multi process mode was implemented incorrectly. So while these "created" metrics were available, there were most likely not correct.

Please see this example highlighting the behavior: https://github.com/trallnag/prometheus-fastapi-instrumentator/tree/master/devel/examples/prom-multi-proc-gunicorn

Also see the documentation: https://github.com/prometheus/client_python#multiprocess-mode-eg-gunicorn

To handle this the client library can be put in multiprocess mode. This comes with a number of limitations:

• Registries can not be used as normal, all instantiated metrics are exported
• Registering metrics to a registry later used by a MultiProcessCollector may cause duplicate metrics to be exported
• Custom collectors do not work (e.g. cpu and memory metrics)
• Info and Enum metrics do not work
• The pushgateway cannot be used
• Gauges cannot use the pid label
• Exemplars are not supported

Not sure if there is a workaround.

[zdets]

Thanks for the clarification.