A rails rack middleware to check the heartbeat, redis & database connection of your rails app

heartbeat.rb

# Rack middleware to return 200 if service is up
#
# Usage:
#
# GET /hb
#
# GET /db
#
class HeartBeat
  OK = [200, {"Content-Type" => "text/plain"}, []].freeze
  KO = [500, {"Content-Type" => "text/plain"}, []].freeze
  HB_PATH = "/hb".freeze
  DB_PATH = "/db".freeze
  PONG = "PONG".freeze

  def initialize(app)
    @app = app
  end

  def call(env)
    case env['PATH_INFO']
    when HB_PATH
      return all_services_up? ? OK : KO
    when DB_PATH
      return database_up? ? OK : KO
    end
    @app.call(env)
  end

  private

  def all_services_up?
    redis_up?
  end

  def redis_up?
    $redis_writer.ping == PONG rescue false
  end

  def database_up?
    ActiveRecord::Base.connection_pool.with_connection { |con| con.active? }  rescue false
  end
end

Nice gist. Is there any importance for line number 27?