Awesome

Adapter for easy exporting your collected metrics from your application to the Prometheus!

One more? Why not X?

https://github.com/discourse/prometheus_exporter – built on assumption that various processes (web, jobs, etc) are able to communicate between them on single machine. But in containerized environments all your processes on different “machines”!
https://github.com/getqujing/prome – actually inspired this all these gems but seems abandoned and lacks extensibility.

Installation

Add this line to your application's Gemfile:

gem 'yabeda-prometheus'

And then execute:

$ bundle

Usage

Exporting from running web servers:

Place following in your config.ru before running your application:
```
use Yabeda::Prometheus::Exporter
```
Metrics will be available on /metrics path (configured by :path option), additionally metrics can be served only on specific port with :port option.

Alternatively you can mount it in Rails application routes as standalone Rack application:
```
Rails.application.routes.draw do
  mount Yabeda::Prometheus::Exporter, at: "/metrics"
end
```
Additional options (like :port) are also accepted and forwarded to Prometheus Exporter middleware.
Run web-server from long-running processes (delayed jobs, …):
```
Yabeda::Prometheus::Exporter.start_metrics_server!
```
WEBrick will be launched in separate thread and will serve metrics on /metrics path.

ATTENTION: Starting from Ruby 3.0 WEBrick isn't included with Ruby by default. You should either add gem "webrick" into your Gemfile or launch Yabeda::Prometheus::Exporter.rack_app with application server of your choice.

See yabeda-sidekiq for example.

Listening address is configured via PROMETHEUS_EXPORTER_BIND env variable (default is 0.0.0.0).

Port is configured by PROMETHEUS_EXPORTER_PORT or PORT variables (default is 9394).
Use push gateway for short living things (rake tasks, cron jobs, …):
```
Yabeda::Prometheus.push_gateway.add(Yabeda::Prometheus.registry)
```
Address of push gateway is configured with PROMETHEUS_PUSH_GATEWAY env variable.

Multi-process server support

To use Unicorn or Puma in clustered mode, you'll want to set up underlying prometheus-client gem to use DirectFileStore, which aggregates metrics across the processes.

Prometheus::Client.config.data_store = Prometheus::Client::DataStores::DirectFileStore.new(dir: '/tmp/prometheus_direct_file_store')

See more information at prometheus-client README.

Aggregation settings

You can specify aggregation policy in gauges declaration:

group :some do
  gauge :tasks do
    comment "Number of test tasks"
    aggregation :max
  end
end

Debugging metrics

Time of already collected metrics rendering in response for Prometheus: yabeda_prometheus_render_duration.

These are only enabled in debug mode. See Yabeda debugging metrics on how to enable it (e.g. by specifying YABEDA_DEBUG=true in your environment variables).

Exporter logs

By default, exporter web server logs are disabled. For example, you can plug in a Rails logger:

Yabeda::Prometheus::Exporter.start_metrics_server! logger: Rails.application.logger

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/yabeda-rb/yabeda-prometheus.

Releasing

Bump version number in lib/yabeda/prometheus/version.rb

In case of pre-releases keep in mind rubygems/rubygems#3086 and check version with command like Gem::Version.new(Yabeda::Prometheus::VERSION).to_s
Fill CHANGELOG.md with missing changes, add header with version and date.

Make a commit:

git add lib/yabeda/prometheus/version.rb CHANGELOG.md
version=$(ruby -r ./lib/yabeda/prometheus/version.rb -e "puts Gem::Version.new(Yabeda::Prometheus::VERSION)")
git commit --message="${version}: " --edit

Create annotated tag:

git tag v${version} --annotate --message="${version}: " --edit --sign

Fill version name into subject line and (optionally) some description (list of changes will be taken from changelog and appended automatically)
Push it:
```
git push --follow-tags
```
GitHub Actions will create a new release, build and push gem into RubyGems! You're done!

License

The gem is available as open source under the terms of the MIT License.