Redirect logger output for a specific controller in Rails 3

Question

We want to have a collection of controllers where we route logger output from all actions and downstream methods to a separate log file. This is a Rails 3 project. In Rails 2 we

Answer 1

The reason that not all the stuff is redirected by controller filter, is that these “Started...” etc are written by rack middleware, that is executed before the controller was even instantiated.

So, to grab and redirect everything related to some condition, one should interfere deeper. Below is a [possibly incomplete] example on how to hack into the pipeline.

Define the middleware to switch loggers

module MyApp
  class MyMiddleware

    def initialize(app)
      @app, @logger = app, Rails.logger
                                .instance_variable_get(:@logger)
                                .instance_variable_get(:@log)
      @my_logger = Logger.new('reports_controller.log', ...)
    end

    def call(env)
      # env['action_dispatch.logger'].inspect
      #⇒  @log_dest=...>

      # here we do not have a controller name
      Rails.logger
           .instance_variable_get(:@logger)
           .instance_variable_set(:@log,
               case env['PATH_INFO'] # or PATH_INFO, or whatever
               when %r|\A/api/v1/| then @my_logger
               else @logger
               end
           )

      @app.call(env)
    end
  end
end

Add an initializer somewhere in config/initializers/my_logger.rb

Rails.application.middleware.insert_before \
    Rails::Rack::Logger, MyApp::MyMiddleware

Please note, that Rails’ logger is a nested beast:

Rails::logger
#⇒ #

One might want to set a specific formatter on the logger, or even filter messages using regular expression there (though it should not be considered a good practice.)