Ventable::Statsd – Easily Track Application Events with Statsd

This library is a small extension to the Ventable eventing library. It provides out of the box support for tracking Ventable events using Statsd.

Why? Because by utilizing Ventable's powerful abstraction you can map the most important events in the system as classes, and then subscribe them all globally to the Statsd collector.

This gem does not depend on any particular implementation of statsd client library, and it expects that you create a statsd client and pass it via the .configure to the Ventable::Statsd.

The client should typically respond to the methods such as increment, gauge, set, measure and expect the metric name and value to be it's parameters. The methods were modelled based on the statsd-instrument ruby gem, but it should be compatible with many others.

The gem works as follows:

1. You configure the backend
2. You register your ventable events to notify Ventable::Statsd
3. You either follow the default naming strategy, or provide your own. See Naming Events further down.

Before we can track our events, let's configure our statsd:

require 'statsd-instrument'
require 'ventable/statsd'

# see https://github.com/Shopify/statsd-instrument for more info
StatsD.backend = StatsD::Instrument::Backends::UDPBackend.new("172.16.0.1:8125", :statsd)

Ventable::Statsd.configure do |config|
  config.statsd = StatsD
  config.enabled = true
end

Now we must connect the event dispatch mechanism with the Ventable::Statsd module:

class ApplicationOpenedEvent
  include Ventable::Event
end

# Subscribe the event to track event dispatch
ApplicationOpenedEvent.notifies Ventable::Statsd

# Now fire the event, and it should send a packet to statsd!
ApplicationOpenedEvent.new.fire!
#=> calls StatsD.increment('application_opened_count', 1)

Or you can register Ventable::Statsd in a super class of all of your application events, so that you don't have to repeat this code:

class AbstractEvent
  def self.inherited(klass)
    klass.instance_eval do
      include Ventable::Event
    end
    klass.notifies Ventable::Statsd
  end
end

class ApplicationOpenedEvent < AbstractEvent; end

The biggest customization lies within the way you might like to map various event occurring to a specific metric name in the Graphite database.

As you might now, when metric name is separated by a dot '.', Graphite create sub-folders and group sub-metrics together. For example order.completed.count and order.cancelled.count would be grouped together under order.* in Graphite.

This is why the default naming scheme uses your event class name, converts it to a lower-case underscored version, and replaces all underscores with a dot (while also removing redundant _event if there). This way, an event named, say UserRegistrationCompletedEvent would be converted to a metric name user.registration.completed.count. Note how the default metric type is count, which would be registered by calling increment(name, 1) on Statsd.

But what if you wanted to customize how metrics are called?

What if you want to keep track of some events as a gauge and not the counter?

In these and other cases, there are two ways to customize the event names. But before we jump in to see how these are configured, let's discuss what these procs are expected to return.

The return of naming customization method/proc is a complete or any portion of the following hash — and here are a couple of examples that hopefully explain how this hash is used by the library:

 # Method to call on statsd; and its value        Metric to pass to Statsd
 { method: :increment, value: 1,           name: 'graphite.metric.name' }
 { method: :gauge,     value: event.total, name: 'graphite.aggregate.gauge' }

You can configure a proc at the top level that receives an event as a parameter, and returns an event naming hash (see above) for a given event. This can be useful if you can write a single proc that covers all of your cases in one place, but is distinct from the default naming.

The argument to the proc or method is the event instance.

Below we provide the metric naming algorithm in the configuration clause for the gem:

Ventable::Stats.configure do |c|
  # this would return a name 'my_event.count' for MyEvent
  c.event_to_metric_proc = ->(event) { { method: :increment,
                                          value:  1,
                                           name:  event.class.name.underscore + '.count' } }
end

You can also configure each event with a class method statsd_config that receives an event instance as an argument, and must return the event naming hash to customize the naming and statsd methods.

While in the previous example above the proc was applied to all events, the following would only apply to the concrete event classes below:

class OrderShippedEvent
  attr_accessor :carrier
  class << self
    def statsd_config
        ->(event) { { method: :increment,
                       value:  1,
                        name:  "order.shipped.#{event.carrier.code}.count" } }
    end
  end                      
end

class OrderReturnStartedEvent
  class << self
    def statsd_config
        ->(*) { { name:  'order.returns.count' } }
    end
  end                      
end

The above examples demonstrate the flexibility of the naming:

1. In the first example, OrderShippedEvent is supposed have carrier accessor, which in turn has a code — presumably returning a short string, one of %w(fedex ups dhl) etc. By using this custom naming scheme we are able to group in Graphite our shipping completions by carrier without having to create a new event class for each carrier type.
2. In the second example we do not care about the event instance, but provide the gem with an alternative name for this event. Note also that we are not including :method or :value, which would then be used from the defaults.

Add this line to your application's Gemfile:

gem 'ventable-statsd'

And then execute:

$ bundle

Or install it yourself as:

$ gem install ventable-statsd

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.

Bug reports and pull requests are welcome on GitHub at https://github.com/kigster/ventable-statsd.

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