flags: add log flags to enable log rotation

[yoomee1313]

Proposed changes

• Next flags are added. They are from go-ethereum flags but --log.format is slightly different from Ethereum.
  • --log.file: If the log file name is passed through the --log.file flag, klaytn code will write the logs at that file.
  • --log.format: It sets the log format (json|logfmt|terminal). Default format is terminal.
  • --log.rotate: If rotate flag is set, klaytn code will write the logs at the log file and supports log rotation.
  • --log.maxsize, --log.maxbackups, --log.maxage, --log.compress: specific log rotation configs. Those flags is used with --log.rotate flag.
• For better usage, log roration related options are added at conf files and those options are supported at klaytn node daemon files.
  e.g. kend.conf

  # log rotation related options
  LOG_ROTATE=0 # setting 1 to enable the log rotation related options
  LOG_MAXSIZE=100 # the unit is MB
  LOG_MAXBACKUPS=10
  LOG_MAXAGE=30 # maximum number of days to retain a log file
  LOG_COMPRESS=1 # setting 1 to compress the backup logs in gz format

• We are using daemon files(e.g. kend) to startup the klaytn process and we were redirecting the all standard outputs to the log files with the logs. We kept the redirection of standard outputs for the consistency.

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Further comments

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[hyunsooda]

How about to add this new feature to doc?

[yoomee1313]

How about to add this new feature to doc?

Correct, I'll update the new flags at here: https://docs.klaytn.foundation/content/operation-guide/log-management

[yoomee1313]

@kjeom @nohkwak Could you approve this PR?