A convenience for formatting logs in logfmt, to be used with the Logger.Backends.Console backend.

To use, specify the {LogfmtEx, :format} tuple in the backend's configuration, replacing the format string:

config :logger, :console,
  format: {LogfmtEx, :format}

logfmt

Logfmt

In logfmt, each line consists of a single level of key=value pairs, densely packed together.

For example:

Logger.info("I am a message", user_id: 123)

given the configuration

config :logger, :console,
  format: {LogfmtEx, :format},
  metadata: [:user_id, :pid, :file]

config :logfmt_ex, :opts,
  message_key: "msg",
  timestamp_key: "ts",
  timestamp_format: :iso8601

would emit:

level=info msg="I am a message" ts="12:38:38.055 1973-03-12" user_id=123 pid=#PID<0.223.0> file=myapp/some_module.exs

configuration

Configuration

Several aspects of the format function can be customized via the application env in a config/config.exs file, under config :logfmt_ex, :opts:

• :delimiter - defaults to =.
• :format - A list of atoms that defines the order in which key/value pairs will written to the log line. Defaults to [:timestamp, :level, :message, :metadata]. Valid parameters are
  • :timestamp - the timestamp of the log message
  • :level - the log level
  • :message - the log message itself
  • :metadata - metadata as key=value paris
  • :node - the node name
• timestamp_key - changes the key used for the timestamp field. Defaults to timestamp.
• timestamp_format - How the timestamp is formatted. Defaults to :elixir. The options are
  • :elixir - Uses the same formatting functions found in the standard elixir log formatter. Example: "12:38:38.055 1973-03-12"
  • :epoch_seconds - outputs an integer representing the number of seconds elapsed since January 1, 1970. Only useful for applications that emit logs sporadically.
  • :iso8601 - Formats the timestamp according to ISO8601-2019. Example: 2000-02-29T23:00:07
• level_key - the key used for the log level. Defaults to level.
• message_key - the key used for the message field. Defaults to message, but msg is a popular alternative.

For encoding your own structs and types, see the LogfmtEx.ValueEncoder protocol.