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LoggerJSON Downloads Latest Version License Build Status Coverage Status SourceLevel

JSON console back-end for Elixir Logger.

It can be used as drop-in replacement for default :console Logger back-end in cases where you use use Google Cloud Logger or other JSON-based log collectors.

Minimum supported Erlang/OTP version is 20.


We deploy our applications as dockerized containers in Google Container Engine (Kubernetes cluster), in this case all your logs will go to stdout and log solution on top of Kubernetes should collect and persist it elsewhere.

In GKE it is persisted in Google Cloud Logger, but traditional single Logger output may contain newlines for a single log line, and GCL counts each new line as separate log entry, this making it hard to search over it.

This backend makes sure that there is only one line per log record and adds additional integration niceness, like LogEntry format support.

After adding this back-end you may also be interested in redirecting otp and sasl reports to Logger (see "Error Logger configuration" section).

Log Format

LoggerJSON provides two JSON formatters out of the box (see below for implementing your own custom formatter).

The LoggerJSON.Formatters.BasicLogger formatter provides a generic JSON formatted message with no vendor specific entries in the payload. A sample log entry from LoggerJSON.Formatters.BasicLogger looks like the following:

  "time": "2020-04-02T11:59:06.710Z",
  "severity": "debug",
  "message": "hello",
  "metadata": {
    "user_id": 13

The other formatter that comes with LoggerJSON is LoggerJSON.Formatters.GoogleCloudLogger and generates JSON that is compatible with the Google Cloud Logger LogEntry format:

    "function":"Elixir.LoggerJSONGoogleTest.test metadata can be configured/1",

Log entry in Google Cloud Logger would looks something like this:


You can change this structure by implementing LoggerJSON.Formatter behaviour and passing module name to :formatter config option. Example module can be found in LoggerJSON.Formatters.GoogleCloudLogger.

config :logger_json, :backend,
  formatter: MyFormatterImplementation


It's available on Hex, the package can be installed as:

  1. Add :logger_json to your list of dependencies in mix.exs:
def deps do
  [{:logger_json, "~> 4.0"}]
  1. Set configuration in your config/config.exs:
config :logger_json, :backend,
  metadata: :all

Some integrations (for eg. Plug) uses metadata to log request and response parameters. You can reduce log size by replacing :all (which means log all) with a list of the ones that you actually need.

  1. Replace default Logger :console back-end with LoggerJSON:
config :logger,
  backends: [LoggerJSON]
  1. Optionally. Log requests and responses by replacing a Plug.Logger in your endpoint with a:
plug LoggerJSON.Plug
  1. Optionally. Use Ecto telemetry for additional metadata:

Attach telemetry handler for Ecto events in start/2 function in application.ex

:ok =
    [:my_app, :repo, :query],

Prevent duplicate logging of events, by setting log configuration option to false

config :my_app, MyApp.Repo,
  adapter: Ecto.Adapters.Postgres,
  log: false

Dynamic configuration

For dynamically configuring the endpoint, such as loading data from environment variables or configuration files, LoggerJSON provides an :on_init option that allows developers to set a module, function and list of arguments that is invoked when the endpoint starts.

config :logger_json, :backend,
  on_init: {YourApp.Logger, :load_from_system_env, []}

Encoders support

You can replace default Jason encoder with other module that supports encode_to_iodata!/1 function and enconding fragments.


The docs can be found at


Many source code has been taken from original Elixir Logger :console back-end source code, so I want to thank all it's authors and contributors.

Part of LoggerJSON.Plug module have origins from plug_logger_json by @bleacherreport, originally licensed under Apache License 2.0. Part of LoggerJSON.PlugTest are from Elixir's Plug licensed under Apache 2.