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Simple::Metrics

A simple JRuby wrapper around Coda’s excellent Metrics package

Installation

Add this line to your application’s Gemfile:

gem 'simple-metrics'

And then execute:

$ bundle

Or install it yourself as:

$ gem install simple-metrics

Healthchecks

Monitor the health of your application in a granular way.

In a Sinatra/Padrino app, register healthchecks as an extension like so:

register Simple::Metrics::Healthchecks

To register a new healthcheck:

class NurseRatched
  extend Simple::Metrics::Healthchecks

  attr_accessor :temp

  new_healthcheck("temperature") do
    if @temp = 98
      Simple::Metrics::HEALTHY
    elsif @temp > 101
      Simple::Metrics::UNHEALTHY.new("Fever!")
    else
      Simple::Metrics::WARNING
    end
  end
end

Run all healthchecks:

NurseRatched.run_all_healthchecks

Your healthchecks will be run in a separate thread every 5 seconds. This is a great way to monitor the health of your db connections, thread pools and connections to queues.

If you are running the servlet in a warbler .war file (see example below), you can monitor the overall health of your application with nagios or other monitoring tools.

Timers

From: Timers:

A timer measures both the rate that a particular piece of code is called and the distribution of its duration.

class Samovar
  include Simple::Metrics

  def buh
    timer("tea time") do
      "Brewing..."
    end
  end
end

Meters

From: Meters:

“A meter measures the rate of events over time (e.g., “requests per second”). In addition to the mean rate, meters also track 1-, 5-, and 15-minute moving averages.”

class Rdio
  extend Simple::Metrics::Meter

  define_meter :bump_meter

  def bump_dat
    bump_meter.mark
  end
end

Send metrics directly to graphite

In a Sinatra app:

register Simple::Metrics::Graphite

enable_graphite_reporter("graphite.example.com", 2003, "services.#{RACK_ENV}")

Exposing metrics from within your app

In order to view/collect the health and metrics of your application from the web, you’ll need to add the servlet endpoints. For this example, I’m using Warbler to package the application as a .war

In config/web.xml, add the following servlet mappings:

  <servlet>
    <servlet-name>metrics.MetricsServlet</servlet-name>
    <servlet-class>com.yammer.metrics.reporting.MetricsServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>metrics.MetricsServlet</servlet-name>
    <url-pattern>/metrics</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>metrics.HealthCheckServlet</servlet-name>
    <servlet-class>com.yammer.metrics.reporting.HealthCheckServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>metrics.HealthCheckServlet</servlet-name>
    <url-pattern>/healthcheck</url-pattern>
  </servlet-mapping>

  <servlet>
    <servlet-name>metrics.ThreadDumpServlet</servlet-name>
    <servlet-class>com.yammer.metrics.reporting.ThreadDumpServlet</servlet-class>
    <url-pattern>/threads</url-pattern>
  </servlet>

  <servlet>
    <servlet-name>metrics.PingServlet</servlet-name>
    <servlet-class>com.yammer.metrics.reporting.PingServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>metrics.PingServlet</servlet-name>
    <url-pattern>/ping</url-pattern>
  </servlet-mapping>

Now you can visit your application and get a thread dump, health check or collect metrics using collectd:

> curl localhost:9292/threads
  main id=1 state=WAITING
  - waiting on <0x073772c5> (a java.lang.Object)
  - locked <0x073772c5> (a java.lang.Object)
  at java.lang.Object.wait(Native Method)