Health
======

Health will setup a standardized health_check URL on your application.  System Administrators can 
then use this URL to look for an HTTP response of 200 and the response content of 'SERVERUP'.

Example
=======

To add the health check to your application you can include this plugin and simply include it in your 
application controller.

  ApplicationController < ActionController::Base
    include Health
  end

Once you've done this you can see if the application is running by navigating to 

  http://localhost:3000/health_check

HINT: Health does not care what controller it is mixed in with.

Database Check
==============

By default, health will also run a basic sql query[1] on your database and check the results.  If there is
an error it will return content of 'DBDOWN'.  NOTE, if your database is down or the credentials are not 
properly setup, Rails will throw a 500 error before the health_check action is ever run.

Some rails applications do not use a databases and are not backed ActiveRecord models.  To turn of the
database check you configure health_check with a option to turn it off:

  ApplicationController < ActionController::Base
    include Health
    health_check :with_db => false
  end

[1] the query it runs is 'select 1' on your ActiveRecord::Base.connection.

Manual Checks
=============

You can also supply any additional checking you'd like to have Health to perform.  This return value +must+ 
be true if successful, otherwise it will return the result after the content 'PROCDOWN'.  You can specify
multiple checks and Health will return once a check fails and will not process any other checks.  

I suggest that if a process fails to return a descriptive reason as the result so you can see why/which check
failed. (ie. PROCDOWN no donut)

You can specify a Proc, block, or a Symbol representing the method name on the controller in which Health 
was included.

For +blocks+, the controller argument is optional:

  ApplicationController < ActionController::Base
    include Health
    health_check do |controller|
      controller.has_donut? || "no donut"
    end
  end

For +Procs+, just past them as a list of arguments, they are run in context of the controller:

  ApplicationController < ActionController::Base
    include Health
    health_check lambda {  donut? || "no donut" }, lambda { donuts.size < 12 || "less than a dozen donuts" }
  end
  
For +Symbols+, make sure they are defined in your controller:

  ApplicationController < ActionController::Base
    include Health
    health_check :check_donut, :check_quantity

    def check_donut
      donut? || "no donut"
    end
    
    def check_quantity
     donuts.size < 12 || "less than a dozen donuts"
    end
  end

You may mix and match all three types, the block will be run last:

  ApplicationController < ActionController::Base
    include Health
    health_check :check_donut, lambda { donuts.size < 12 || "less than a dozen donuts" }, :with_db => false do |c|
      c.homer.blank? || "watch out for homer"
    end
    
    def check_donut
      donut? || "no donut"
    end
  end

Copyright (c) 2008 Los Angeles Times, released under the MIT license