Auto rotating logs by file size

Are you using journalctl?

You can set time or size limits for rotation, deletion

Yes you can, by the way of Erlang/OTP logging handler :logger_disk_log_h. The relevant documentation is in Logger and Erlang

You need to mentally combine the two doc in your head to have the complete picture.

Also you should keep a less chatty log to the console for your own good, use the OS provided facilities to rotate it. Keep the chatty log separate from the default and do whatever you want on this one.

Thanks for the suggestion. Here’s my latest attempt:

# config.exs
import Config

config :myapp, :logger,
  [
    {:handler, :default, :logger_disk_log_h, %{level: :info, file: 'test.log', max_no_bytes: 100_000_000}}
  ]

config :logger,
  utc_log: true,
  backends: [
    {LoggerFileBackend, :warnings_log},
    {LoggerFileBackend, :info_log}
  ]

config :logger, :warnings_log,
  path: "/home/myapp/Logs/warnings.log",
  level: :warn

config :logger, :info_log,
  path: "/home/myapp/Logs/info.log",
  level: :info

# application.ex
defmodule MyApp.Application do
  require Logger
  use Application

  def start(_type, _args) do
    :logger.add_handlers(:myapp)

    Logger.info("Initiating My App \n")
  end

Logs still don’t auto-rotate. What did I miss?

Read carefully here, it is a map within a map.
Also I do not suggest you change the :default handler. I am not sure if it is possible.

What I meant is:

config :myapp, :logger,
  [
    {:handler, :my_disk_log, :logger_disk_log_h,
         %{config: %{file: 'test.log',
                     max_no_bytes: 100_000_000},
           level: :info}
    }
  ]

Untested, but you get the idea. It is a 2 level map, and each have it own set of keys. The outer level is the general configuration for any log_handler, the inner one is the configuration specifically for :logger_disk_log_h

Success!

Here’s the new config:

config :myapp, :logger, [
  {:handler, :myapp_disk_log, :logger_disk_log_h,
   %{
     config: %{file: 'Logs/info.log', max_no_bytes: 100_000_000},
     level: :info,
     formatter_config: %{time_offset: 0}
   }}
]

config :logger,
  utc_log: true,
  backends: [
    {LoggerFileBackend, :info_log}
  ]

Now, based on what the manual indicates here and here, formatter_config: %{time_offset: 0} was added to set the timestamp to UTC. However, this is not working. Where did I go wrong?

for formatter, it should be a map inside a tuple:

    formatter: {:logger_formatter, %{...}}

This thing is designed to be VERY flexible and powerful. Not the easiest API to use

Changed formatter_config: %{time_offset: to formatter: {:logger_formatter, %{time_offset: 0} and now logs are being recorded in UTC. (Also got rid of utc_log: true,)

Thanks for helping translate the Erlang into Elixir

Do not listem to @derek-zhou and do not use :logger_disk_log_h. That one is left for compatibility reasons and :logger_std_h instead. It works better and in more reasonable way.

Care to elaborate more? I am still using Erlang 21 and :logger_std_h in 21 does not support circular log file rotation.