Cookbooks
Elixir
Chapter 5. Good Coding Practices
Logging

Elixir:
Logging

How to:

In Elixir, the primary way to log information is through the built-in Logger module. Here’s how you can use it:

defmodule MyApplication do
  require Logger

  def do_something_important(param) do
    Logger.info("Starting important process with param: #{param}")

    # Simulate work being done
    :timer.sleep(1000)

    Logger.debug("Process completed.")
  rescue
    error -> Logger.error("An error occurred: #{inspect(error)}")
  end
end

# To see your logs, you just call the function:
MyApplication.do_something_important("MyParam")

This simple snippet shows how to log at different levels (info, debug, and error). When you run this, you won’t see the debug message unless you configure the Logger level to :debug. By default, Elixir’s Logger filters out log messages below :info.

Sample output at the :info level might look like this:

14:32:40.123 [info]  Starting important process with param: MyParam
14:32:41.126 [error] An error occurred: %RuntimeError{message: "runtime error"}

Deep Dive:

Elixir’s Logger is a built-in tool that’s been part of the language since its early days. It is influenced by the logging systems from other BEAM languages like Erlang. The logger provides different levels of logging – :debug, :info, :warn, and :error – and it’s pluggable, allowing different backends to be hooked in for handling log messages.

One alternative to the built-in Logger for more complex scenarios is the use of logging libraries such as Logstash or Sentry for Elixir, which can provide additional features like error tracking and aggregation in a more visual format. For local development, Elixir developers often rely on built-in Logger functionality for its simplicity and integration with the BEAM VM.

Under the hood, the Logger module offers asynchronous and synchronous logging. Asynchronous logging, which is the default, does not block the execution of your application while logging the messages. This ensures that logging does not negatively affect performance. However, synchronous logging can be enabled for cases where you need to guarantee that messages are logged in the order they were sent.

The Logger configuration can be adjusted in the config/config.exs file of an Elixir application, where you can set the logging level, format, metadata, and more. Always remember to adjust your logging levels and outputs for different environments; you wouldn’t want verbose debug logs flooding your production systems.

See Also:

Handling errorsOrganizing code into functions