Exposing metrics not hosted via starlette

[Matthew D. Scholefield]

Often in a production application one might want to hide the /metrics endpoint from public traffic. Using the methods listed in the README, one would have to explicitly mask the /metrics route within a reverse proxy and bind to two different ports which can be non-trivial (see encode/uvicorn#571 for context).

In my experience I've found it easier to just expose the metrics on a separate port (Ie. 9090) via Prometheus's default start_http_server function but I'm not sure if this is supported by starlette-exporter. This way the metrics requests are served completely internally (and, for example, can only be exposed internally within a kubernetes cluster). While probably not necessary, to be clean I also integrated the server used in start_http_server with starlette's lifespan events (otherwise I'm worried for example the socket won't unbind for some period of time when hot reloading).

My questions are (edit: updated questions):

1. Is this supported/possible?
2. Would an example that uses start_http_server be accepted into the README?
3. Would code that calls start_http_server handling lifespan hooks be accepted as a contribution?

cc @NargiT

[Steve Hillier]

Good question. The middleware isn't tied to any particular endpoint, so you could skip adding the /metrics route and provide your own implementation as far as I know. The handle_metrics handler function is just a way to expose prometheus_client.CollectorRegistry().

Any contributions welcome! 👍

[Ionut Popovici]

I will try something on this but will be slow .. but I have an idea what can it be done .
Is not a promise but when I will try some stuff and come back if I have something successful .

[Ionut Popovici]

Found a way .. but need to find a way to do the testing .
When I try to start the server on specific port on testing is not working.
See:
https://github.com/intelroman/starlette_exporter/blob/master/starlette_exporter/__init__.py
Worked for me in FastAPI

[Steve Hillier]

This issue is getting old and I'm doing some clean up. The metrics can be exposed any way that Prometheus supports, and is not limited by starlette_exporter. Please reopen if there's more to discuss.