Call for testers: new Elixir Logger backend

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Very excited about this. Thanks for all your work!

I’m curious what approach you have in mind for structured logging. So far I’ve been doing it this way:

  • At the call site, pass structured data via metadata:
      Logger.log(level, "Processing request",
    method: conn.method,
    path: conn.request_path,
    ...
  )
  • Define a custom formatter which takes all metadata:
    config :logger, :file_log,
  path: "app.log",
  level: :info,
  format: {MyApp.Logger, :format},
  metadata: :all
  • In the formatter, generate JSON, roughly like:
    def format(level, message, timestamp, metadata) do
 %{
    "timestamp" => format_timestamp(timestamp),
    "level" => level,
    "message" => IO.iodata_to_binary(message)
  }
  |> add_metadata(metadata)
  |> Jason.encode!()
end
    where add_metadata reads each key/value pair from metadata, converts the value to a printable representation, and adds it to the event map, similar to Honeybadger.JSON.

It works, but it’s not ideal - we had to reimplement functionality from the default formatter, for instance formatting time or converting PIDs to strings. OTP reports also can’t be structured, because they’re a string blob by the time they reach the formatter (not a huge deal though).

Could we achieve JSON logging more easily with the new backend, or with future development?

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