Rails connection management to handle Amazon Aurora's failover

application.rb

module xxx
  class Application < Rails::Application

   #（中略）

    config.middleware.swap ActiveRecord::ConnectionAdapters::ConnectionManagement,
                           'ActiveRecord::ConnectionAdapters::ReconnectOnErrorManagement'
  end
end

reconnect_on_error_management.rb

module ActiveRecord
  module ConnectionAdapters
    class ReconnectOnErrorManagement
      CONNECTION_ERROR = ['Lost connection', 'gone away', '--read-only']
      CONNECTION_ERROR_RE = /#{CONNECTION_ERROR.map{|w|Regexp.escape(w)}.join('|')}/
      CONNECTION_ERROR_RE.freeze

      def initialize(app)
        @app = app
      end

      def call(env)
        testing = env.key?('rack.test')

        response = @app.call(env)
        response[2] = ::Rack::BodyProxy.new(response[2]) do
          ActiveRecord::Base.clear_active_connections! unless testing
        end

        response
      rescue Exception => e
        unless testing
          if should_clear_all_connections?(e)
            ActiveRecord::Base.clear_all_connections!
          else
            ActiveRecord::Base.clear_active_connections!
          end
        end
        raise
      end

      def should_clear_all_connections?(e)
        if e.kind_of?(ActiveRecord::StatementInvalid)
          return CONNECTION_ERROR_RE === e.message
        end
        return false
      end
    end
  end
end