A Rack middleware to send HTTP metrics via StatsD. A building block toward achieving Grafana Dashboard like below for a Ruby web server.

The middleware exports two metrics:

• rack_server_request_duration_seconds - a histogram representing the latency of an HTTP request with the following labels:

  • code - the response code
  • method - the request method
  • path - the request path; stripped from any identifiers, for eg. /resource/45646 becomes /resource/:id

• rack_server_exceptions_total - a counter of unhandled exceptions with the following label:

  • exception - the class name of the error (error.class.name)

1. Add this gem to your application:

bundle add statsd-rack-instrument

2. Add to your config.ru

if ENV["STATSD_ADDR"].present?
  require "statsd_rack_instrument"
  use StatsDRackInstrument
end

run Rails.application # or other command for starting the app

3. Provide necessary env vars

• STATSD_ADDR - the address of the StatsD collector
• STATSD_ENV - should be set to production; if not provided, then StatsD will fallback to RAILS_ENV or ENV

Check Configuration section from the statsd-instrument gem for more info.

When combined with statsd_exporter it is possible to get exported metrics into Prometheus. Check out "Collecting Prometheus metrics from multi-process web servers, the Ruby case" blog post discussing the idea and how to achieve it.