JSON output as prometheus metric format?

[Ekleog]

Hey!

I've been using rustic for a bit, and I recently submitted [a module for easily using it to NixOS](https://github.com/NixOS/ nixpkgs/pull/373042) (my personal distribution of choice).

As part of it, I added one thing useful at least to me: parsing the JSON output of --json and turning it into prometheus metrics that could then be exported via the node-exporter.

But upon thinking about it some more I'm curious: are you interested in upstreaming this work, so that rustic could gain a --prometheus flag that'd output the result as prometheus metrics, rather than raw JSON?

TBH the JSON currently output is not very nice to work with, eg. because parsing times (esp. when TZ is not UTC) is hard — hence the hacks used in the NixOS module's script to work around it.

WDYT?

Anyway, thank you for all you're doing with rustic!

[aawsome]

Hi @Ekleog, thanks for opening this issue!

I agree that better prometheus support can be a good addition to rustic. IMO for the rustic CLI we should try to support prometheus push gateway. I had just a quick view into available crates, but it seem that prometheus crate is widely used and supports this via the push feature.

About the metrics: @Ekleog Can you please specify a list which metrics you would send to the push gateway?

Is there anyone willing to start a PR?

[Ekleog]

I just opened #1404 ; hopefully it makes it more obvious which exact metrics I'd like to send to the pushgateway!

It's basically all the (numeric, as prometheus only allows numeric metrics) metrics exposed by the JSON output, with timestamps encoded, as prometheus expects, as an f64.

WDYT about it? :)