LoggerJSON

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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.

Motivation

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 backed makes sure that there is only one line per log record and adds additional integration niceness, like LogLine 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

By default, output JSON is compatible with Google Cloud Logger format with additional properties in serviceLocation and metadata objects:

  {
     "time":"2017-04-09T17:52:12.497Z",
     "severity":"DEBUG",
     "sourceLocation":{
        "moduleName":"Elixir.LoggerJSONTest",
        "line":62,
        "functionName":"test metadata can be configured to :all/1",
        "file":"/Users/andrew/Projects/logger_json/test/unit/logger_json_test.exs"
     },
     "metadata":{
        "user_id":11,
        "dynamic_metadata":5
     },
     "logMessage":"hello"
  }

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

Installation

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

  1. Add :logger_json and :poison to your list of dependencies in mix.exs:

    def deps do [{:poison, “~> 3.1”}, {:logger_json, “~> 0.4.0”}] end

  2. Ensure logger_json and :poison is started before your application:

    def application do [extra_applications: [:poison, :logger_json]] end

  3. Set a :json_encoder in your config/config.exs:

    config :logger_json, :backend, json_encoder: Poison

  4. Replace default Logger :console back-end with LoggerJSON:

    config :logger, backends: [LoggerJSON]

    Poison can be replaced by any other compatible encoder, see “Encoders support” section.

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 Poison encoder with other module that supports encode!/1 function. This can be even used as custom formatter callback.

Popular Poison alternatives:

If your application is performance-critical, take look at jiffy.

Documentation

The docs can be found at https://hexdocs.pm/logger_json

Thanks

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.