How to make each unicorn worker of my Rails application log to a different file?

Question

How can I make each unicorn worker of my Rails application writting in a different log file ?

The why : problem of mixed log files... In its default configuration, Rails will write its log messages to a single log file: log/<environment>.log.

Unicorn workers will write to the same log file at once, the messages can get mixed up. This is a problem when request-log-analyzer parses a log file. An example:

Processing Controller1#action1 ...
Processing Controller2#action2 ...
Completed in 100ms...
Completed in 567ms...

In this example, what action was completed in 100ms, and what action in 567 ms? We can never be sure.

Answer 1

add this code to after_fork in unicorn.rb:

#one log per unicorn worker
if log = Rails.logger.instance_values['log']
  ext = File.extname log.path
  new_path =log.path.gsub %r{(.*)(#{Regexp.escape ext})}, "\\1.#{worker.nr}\\2"
  Rails.logger.instance_eval do
    @log.close
    @log= open_log new_path, 'a+'
  end
end

Answer 2

@slact's answer doesn't work on Rails 3. This works:

after_fork do |server, worker|

  # Override the default logger to use a separate log for each Unicorn worker.
  # https://github.com/rails/rails/blob/3-2-stable/railties/lib/rails/application/bootstrap.rb#L23-L49
  Rails.logger = ActiveRecord::Base.logger = ActionController::Base.logger = begin
    path = Rails.configuration.paths["log"].first
    f = File.open(path.sub(".log", "-#{worker.nr}.log"), "a")
    f.binmode
    f.sync = true
    logger = ActiveSupport::TaggedLogging.new(ActiveSupport::BufferedLogger.new(f))
    logger.level = ActiveSupport::BufferedLogger.const_get(Rails.configuration.log_level.to_s.upcase)
    logger
  end
end