Unicorn is a high-performance forking Web server that is often used for serving Ruby on Rails applications.
Many times, its logging configuration leads implementors to re-instantiate Rails’
logger object, and in the process, to unintentionally log at
DEBUG log level (with SQL statements, cache hits, and other events that are often not necessary).
Here’s how to change the log level of a Rails app served by Unicorn.
Unicorn doesn’t load
Rails::Rack::LogTailer, which is what outputs most Rails logs to
STDOUT. This isn’t an inherent problem, it’s simply a different approach to logging.
Often this leads someone to instantiate a new
Logger in the environment-specific Rails initializer which in the process sets the log level to
Here’s how to replicate similar behavior as exists with most other Rails Web servers.
To output logs to
STDOUT and define the log level, edit
config/environments/<environment>.rb, such as
production.rb. In the
MyApp::Configuration.configure .. end block, add these 3 lines:
config.logger = Logger.new(STDOUT) config.logger.level = Logger.const_get('INFO') config.log_level = :info
These create a new
Logger class that outputs to
STDOUT, then changes the logging level in that newly-instantiated
logger (to an integer, as returned by
Finally, it sets Rails’
log_level to the equivalent symbol so that any other callers, such as Heroku’s
rails_12factor gem, also see the updated level (example: rails_stdout_logging).
Comment out any existing assignments of
config.log_level in the file.
The example above creates a new logger (to
STDOUT) and sets its log level. If you want to leave the log destination as-is and only change its log level, use this instead of the lines above:
config.logger.level = Logger.const_get('INFO') config.log_level = :info
Instead of redefining
config.logger and setting its
level, this simply sets
level on the existing
To set the log level as an environment variable (like when using Heroku config variables), use this instead of the lines above:
config.logger = Logger.new(STDOUT) config.logger.level = Logger.const_get(ENV['LOG_LEVEL'] ? ENV['LOG_LEVEL'].upcase : 'INFO') config.log_level = (ENV['LOG_LEVEL'] ? ENV['LOG_LEVEL'].downcase : 'info').to_sym
This will use the
LOG_LEVEL environmental variable when it is set and
INFO when it is not set.
When a Rails app is deployed, Heroku injects rails_log_stdout, which redefines Rails’
Logger so all output goes to
STDOUT. This doesn’t work as expected with Unicorn, so only rack output is logged.
To re-enable logging to
STDOUT like Heroku expects, use the example in Read log level from env variable above.
heroku config:add to set the desired log level of the Heroku app. For example:
$ heroku config:add LOG_LEVEL="warn"
The app will restart immediately at the new log level.
Optionally, you can tell Heroku not to inject rails_log_stdout since it’s no longer relevant with Unicorn.
To do so, create an empty
vendor/plugins/rails_log_stdout/ directory containing a placeholder file and commit it to your git repo:
$ mkdir -p vendor/plugins/rails_log_stdout $ touch vendor/plugins/rails_log_stdout/keep_me $ git add vendor/plugins/rails_log_stdout/keep_me $ git commit -m "Placeholder file to disable rails_log_stdout" vendor/plugins/rails_log_stdout/keep_me