[deb/rpm] Deprecation warnings caused by legacy logger

[jbudz]

OS Packages make use of the legacy logger by setting logging.dest -

kibana/src/dev/build/tasks/os_packages/service_templates/systemd/usr/lib/systemd/system/kibana.service

Line 18 in dd9dd52

ExecStart=/usr/share/kibana/bin/kibana --logging.dest="/var/log/kibana/kibana.log" --pid.file="/run/kibana/kibana.pid"

This setting was deprecated in 7.13.0 - #94238 and causes console warnings now. Using the new logging configuration changes the logging format and [1]still logs to stdout (for now).

[1]https://www.elastic.co/guide/en/kibana/current/logging-settings.html#logging-settings

When you switch to the new logging configuration, you will start seeing duplicate log entries in both formats. These will be removed when the default appender is no longer required.

logging:
  appenders:
    file:
      type: file
      fileName: kibana.log
      layout:
        type: pattern
  root:
    appenders: [default, file]

We don't want to break the logging format in 7.x, so it looks like the way forward is to continue using the deprecated logger in 7.x. @elastic/kibana-core does this make sense? Looking for recommendations on how we want to approach this

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[lukeelmers]

We don't want to break the logging format in 7.x, so it looks like the way forward is to continue using the deprecated logger in 7.x.

Using the new configuration will have no effect other than to introduce additional/duplicate logs to the same log file in the new format. It will not remove logs in the legacy format.

We decided we would not consider this a true breaking change as the legacy logs weren't removed -- although it is somewhat of a grey area (e.g. it would impact folks relying on grok patterns for parsing & ingesting kibana logs, but we decided this was an acceptable trade off)

[jbudz]

Resolved with #111192 in 8.0. We don't want to break the log format in 7.x, so we'll have to leave the deprecation warning in.