Provide separate Rails log files for each Unicorn worker

1 - explanation.markdown

See http://jordan.broughs.net/archives/2014/09/provide-separate-rails-log-files-for-each-unicorn-worker

2 - unicorn-config.rb

after_fork do |server, worker|
  # This log hack provides separate log files for each unicorn worker.
  # Since Unicorn forks worker processes after loggers are already initialized, by this point other
  # things (like ActiveRecord::Base.logger) are already pointing directly at the current
  # Rails.logger instance so we can't just point `Rails.logger` elsewhere.
  logdev = Rails.logger.instance_variable_get(:@logdev)

  ext = File.extname(logdev.dev.path)
  path = logdev.dev.path.gsub /#{Regexp.escape(ext)}$/, ".#{worker.nr}#{ext}"

  # open the file in the same way rails does:
  #   https://github.com/rails/rails/blob/4606e75/railties/lib/rails/application/bootstrap.rb#L38-L40
  file = File.open(path, 'a')
  file.binmode
  file.sync = Rails.application.config.autoflush_log

  logdev.dev.flush
  logdev.dev.close
  logdev.instance_variable_set(:@dev, file)
end

This worked just right for a rails 4 application I am working on above all different solutions I've tried. Commenting here for visibility.