expose prometheus metrics

[djs55]

Now that metrics have been defined for things like

• bytes read/written/discarded
• bytes of user data
• bytes erased/copied/flushed/referenced

It would be nice to be able to easily expose the metrics via the connect API. For example, if the metrics are scraped by prometheus and graphed by grafana:

[talex5]

Why does connect need changing? The metrics should be exposed automatically by the prometheus library.

[djs55]

I'm looking for a nice place to put this code:

            let module Server = Prometheus_app.Cohttp(Cohttp_lwt_unix.Server) in
            let mode = `TCP (`Port 9090) in (* FIXME: Unix socket *)
            let callback = Server.callback in
            let server = Cohttp_lwt_unix.Server.make ~callback () in
            Lwt.async (fun () -> Cohttp_lwt_unix.Server.create ~mode server);

My particular use-case is a bit funny because the main application (moby/hyperkit) is written in C and uses this code via an OCaml function calling shim.

Maybe I should think of the OCaml shim as being more like a main function rather than just a means of calling read and write and stick the initialisation code there.

(Partly I wanted to create an issue somewhere with a screenshot that I can point people at since I think it looks quite nice!)

[talex5]

Yes, makes sense to keep this out of the API I think.

[samoht]

(Partly I wanted to create an issue somewhere with a screenshot that I can point people at since I think it looks quite nice!)

This looks indeed very nice :-)