[RFC] Align Ruby client with Prometheus best practices, prepare for multi-process support

[prometheus]

[RFC] Align Ruby client with Prometheus best practices, prepare for multi-process support

[Eric-Fontana-Bose]

YES PLEASE!

[SamSaffron]

Having implemented https://github.com/discourse/prometheus_exporter one of the weakest point the official library has is the Summary implementation, it just uses estimates which make all results pretty nonsensical. Other weaknesses are lack of multi process support which is enormous, lack of standard instrumentation people can easily lean on and lack of standalone robust web server implementation short of mounting rack.

I highly recommend any work on improving the default library has a look at the prom exporter implementation for ideas, there is a lot there and the thing is very battle tested.

[dmagliola]

@SamSaffron Thank you for your comments! These are all very good points.

the Summary implementation, it just uses estimates

Yeah, we're actually proposing "downgrading" the Summary to the level which Python offers, which is just having Sum and Count, without quantiles, which is the minimum the Best Practices require. We're doing this for practical reasons, since we want to be able to only store Floats in our stores, and the Quantile::Estimator doesn't play well with that.
Here's the relevant commit

Lack of multi process support

This is the main thing we're aiming at improving with this work. We're currently leaning more towards a "shared memory" implementation (an example of which can be seen in Gitlab's implementation, or in the Python client), but it'd be quite easy for someone to have a store that pushes things to your Collector process.

lack of standard instrumentation people can easily lean on and lack of standalone robust web server implementation short of mounting rack.

We're also planning on looking at these, if we have time, but they're a bit more long-term plans, for now, we're focusing on solving the multi-process issue

[dmagliola]

Update: We've updated PR #95 with actual data stores, including one that works for pre-fork servers 🎉
We'd love everyone's comments on this!

[dmagliola]

All of this is done now that we've merged PR #95