Unicorn after_fork block to have Rails write logs to a separare file for each worker.

unicorn.conf.rb

after_fork do |server, worker|
  log_path = Rails.root.join('log',"#{Rails.env}.#{worker.nr}.log")

  new_logger = Logger.new(log_path)
  new_logger.level = Logger::INFO

  Rails.logger.flush
  Rails.logger.close
  Rails.logger = Rails.application.config.logger = ActiveSupport::TaggedLogging.new(new_logger)

  ActiveSupport::Dependencies.logger = Rails.logger
  ActiveRecord::Base.logger          = Rails.logger
  ActionController::Base.logger      = Rails.logger
  ActionMailer::Base.logger          = Rails.logger
  Rails.cache.logger                 = Rails.logger

  ActiveRecord::Base.establish_connection
end

Thanks, man!