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

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

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