Fix default value of rotate_age

[daipom]

It seems that the old value came from ServerEngine.

• https://github.com/treasure-data/serverengine/blob/v2.3.1/lib/serverengine/daemon_logger.rb#L33

However, actually, ServerEngine has nothing to do with the rotation, and this value 5 is not used at all.

Actually, Logger::LogDevice manages the rotation, and the default value is 7.

• https://github.com/ruby/logger/blob/v1.5.3/lib/logger/log_device.rb#L20

In Fluentd code, the parameters of Fluent::LogDeviceIO decides the behavior of the rotation.

• https://github.com/fluent/fluentd/blob/v1.15.3/lib/fluent/supervisor.rb#L563

The parameters of ServerEngine::DaemonLogger is meaningless.

• https://github.com/fluent/fluentd/blob/v1.15.3/lib/fluent/supervisor.rb#L580-L582

Reproduce

• Env
  • Ubuntu Focal
  • Ruby 3.2
  • Fluentd 1.15.3
• Config
  • default rotate_size

  <system>
    <log>
      rotate_size 500
    </log>
  </system>
  
  <source>
    @type sample
    tag test.hoge
    sample {"message": "hoge"}
  </source>
  
  <match test.**>
    @type stdout
  </match>

  • rotate_size 5

  <system>
    <log>
      rotate_size 500
      rotate_age 5
    </log>
  </system>
  
  <source>
    @type sample
    tag test.hoge
    sample {"message": "hoge"}
  </source>
  
  <match test.**>
    @type stdout
  </match>

• Result
  • default rotate_size: 7 files are created

  fluentd.log
  fluentd.log.0
  fluentd.log.1
  fluentd.log.2
  fluentd.log.3
  fluentd.log.4
  fluentd.log.5
  

  • rotate_size 5: 5 files are created

  fluentd.log
  fluentd.log.0
  fluentd.log.1
  fluentd.log.2
  fluentd.log.3
  

The last index of 7th file is 5.
I think it was hard to notice this mistake because of this.

[ashie]

Thanks!

[daipom]

Thanks for your review!