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Rails Stdout Logging

Rails gem to configure your app to log to standard out.

Build Status


  • Rails 3
  • Rails 4


In your Gemfile add:

gem 'rails_stdout_logging'

Then run

$ bundle install

You also need the rails_serve_static_assets gem. You can get both of them together by installing the rails_12factor gem.

Why is this needed?

By default Rails writes its logs to a file, which is convenient because you only have one log file to tail. When you start scaling your app to multiple machines or dynos, it becomes much harder to find a single request or failure as they're spread across multiple files. Storing logs on disk can also take down a server if the hard drive fills up. Because of these limitations, every Rails core member we talked to uses a custom logger to replace Rails' default functionality. By using the rails_stdout_logging gem with Heroku, we set the logger for you.

The gem rails_stdout_logging ensures that your logs will be sent to standard out. From there, Heroku sends them to logplex so you can access them from the command line like $ heroku logs --tail, or from enabled addons like papertrail. By using Heroku's logplex, you can treat logs as event streams.

Why didn't I need this before?

Why do you need to include this gem in Rails 4 and not Rails 3? Rails4 is getting rid of the concept of plugins. Before libraries were easily distributed as Gems and in the form of Engines, Rails had a folder vendor/plugins. Any code you put there would be initialized much like a Gem is today. This was a very simple and easy way to share and use libraries, but it wasn't very maintainable. You could use a library, and make a change locally and then deploy which makes your version incompatible from future versions. Even worse there was no concept of versioning aside from source control, so semantic versioning was out of the question. For these reasons and more Rails3 deprecated plugins. With Rails4 plugins have been removed completely. Why does this affect your app on Heroku?

In the past Heroku has used plugins as a safe way to configure your application where code was needed. While we advocate separating config from code, this was the only option if we wanted your apps to work with no changes from you. With Rails3 Heroku will add the asset serving and standardout logging plugins to your app automatically. With Rails4, Heroku needs you to add these libraries to your Gemfile.

It is important to note that unlike Gems, plugins do not have a dependency resolution phase like what happens when you run bundle install. Heroku does not and will not add anything to your Gemfile on compilation.

Set log level

On Heroku you can set your log level by using the LOG_LEVEL environment variable

$ heroku config:set LOG_LEVEL=DEBUG

Valid values include DEBUG, INFO, WARN, ERROR, and FATAL. Alternatively you can set this value in your environment config:

config.log_level = :debug

If both are set LOG_LEVEL will take precedence.


Since we're playing with stdout we need to capture stdout. If you want to use the non captured version use DEBUG_STDOUT instead. The puts method should still behave as you expect.

We're using appraisal to build multiple gemfiles for different versions of Rails.

You can run all tests by running

$ bundle exec rake appraisal test

The Future

We will be working with Rails and the Rails core team to make future versions of Rails work on Heroku out of the box. Until then you'll need to add this gem to your project.

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