Ollie

Ollie is a micro-library for building checks that the environment your application runs in is looking ok. It reports on how the systems your app depends on are performing with more granularity than everything-is-swell or everything-is-failing.

Here's an example of the kind of output Ollie would generate at /server-status when reporting on git and redis:

{
    "git": {
        "revision": "9c2a82a968bfc62d8d5c9fb5a947ec58a43f1560",
        "tag": "deploy",
        "branch": "master",
        "updated_at": "2013-02-14T10:39:31-08:00",
        "errors": []
    },
    "redis": {
        "last_restart": "2013-02-14T10:39:31-08:00",
        "failed_jobs": 0,
        "pending_jobs": 100,
        "errors": []
    }
}

Ollie is even more useful when hooked up to an external monitoring system, like Circonus, as it can view trends within the application over time and alert appropriate people when a problem is impending. You can make Ollie most useful by reporting on numbers over true or false / errors or no-error states.

Using Ollie with your app

First, include the gem in your Gemfile:

gem 'ollie', git: '[email protected]:modcloth-labs/ollie.git'

Next, create the controller and route to where you would like Ollie to perform its checking. You might call this StatusController:

class StatusController < ActionController::Base
  include Ollie::Controller
end

Ensure routes are setup to route to that controller:

Persona::Application.routes.draw do
  get 'server-status', to: 'status#server_status'
  #...
end

Finally, indicate what you'd like Ollie to report on:

class StatusController < ActionController::Base
  include Ollie::Controller
  report_on :git, :redis
end

That's it, Ollie is now setup to report on your app.

Writing New Checks

Let's walk through writing a check of a log called status.

All checks need to be in the Ollie namespace and be children of Ollie::Base, in status_logger.rb so we start with:

module Ollie
  class StatusLogger < Ollie::Base
  end
end

You indicate which metrics ollie should report on by declaring them with the metric class method like this:

module Ollie
  class StatusLogger < Ollie::Base
  	metric :file_size
  end
end

Declaring a metric is a promise that a method exists with the same name:

module Ollie
  class StatusLogger < Ollie::Base
  	metric :file_size
  	
	def file_size
		File.size("status.log")
	end
  end
end

If a metric fails it should raise and error. The error's string representation will be returned in the errors key. In the above example, if the file doesn't exist an error will be raised: No such file or directory - status.log

Adding Checks to Your Controller

To add a check to your controller, use the report_on class method:

class StatusController < ActionController::Base
  include Ollie::Controller
  report_on :git, :redis, :status_logger
end

Make sure that YourWonderfulCheck is represented as your_wonderful_check

Author

Ollie was started by Nick Rowe in February 2013.

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How's the weather Ollie?