GreekFire

Prometheus metrics for rails.

Usage

How to use my plugin.

Installation

Add this line to your application's Gemfile:

gem 'greek_fire'

And then execute:

$ bundle

Or install it yourself as:

$ gem install greek_fire

Mount the engine

config/routes.rb:

mount GreekFire::Engine => '/metrics'

Add yer metrics

config/initializers/greek_fire.rb:

GreekFire::Gauge.register "a_generic_metric" do
  GenericModel.where('created_at > ?', Time.zone.now.advance(minutes: -1)).count
end

GreekFire::Gauge.register "another_generic_metric"
                         description: "describes the metric",
                         labels: {:a_label: [1, 2], b_label: "foo"} do | labels |
  AnotherModel.where('created_at > ?', Time.zone.now.advance(minutes: -1)).count
end

GreekFire::Gauge.register "sidekiq_job_latency",
                          description: "How long are jobs enqueued",
                          labels: { :queue => Proc.new { Sidekiq::Queue.all.map(&:name) }} do | labels |
  Sidekiq::Queue.new(labels[:queue]).latency
end


GreekFire::Gauge.register "sidekiq_job_count",
                          description: "How many jobs are enqueued",
                          labels: { :queue => Proc.new { Sidekiq::Queue.all.map(&:name) }} do | labels |
  Sidekiq::Queue.new(labels[:queue]).size
end

Metrics API

The api for creating metrics.

Currently only gauge and counter types of metrics are supported, but other metrics are a PR away!

Gauges

module GreekFire
  class Gauge
    def self.register(name, description:nil, labels:nil, &block)
      ...
    end
  end
end

To register a Gauge (point in time value) call the above method.

Counters

module GreekFire
  class Counter
    def self.register(name, description:nil, labels:nil, &block)
      ...
    end
  end
end

To register a Counter (point in time value) call the above method.

Labels

Labels are a hash of label_name to label_value(s). A label_value may be a collection of values for the labels, or a Proc that returns a collection of label values.

The cross product of all possible label values are used to call the given block.

For example, a gauge with the following labels:

{a_label: [1, 2], b_label: Proc.new { ["some", "list"] }, c_label: "c" }

would have it's block called one for each of the following hashes:

{a_label: 1, b_label: "some", c_label: "c" }
{a_label: 1, b_label: "list", c_label: "c" }
{a_label: 2, b_label: "some", c_label: "c" }
{a_label: 2, b_label: "list", c_label: "c" }

If the label_value is a Proc, the Proc will be called each time metrics are requested. This should allow you to export metrics across label dimentions that change as your app runs. In the installation example you can see that the sidekiq_job_count and sidekiq_job_latency gauges will have a metrics produced for each queue the app is using.

Contributing

1. Fork
2. Write tests.
3. Implement new feature.
4. Create a PR.

License

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