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).

By-default, generated JSON is compatible with Google Cloud Logger LogEntry format:

{
  "log":"hello",
  "logging.googleapis.com/sourceLocation":{
    "file":"/os/logger_json/test/unit/logger_json_test.exs",
    "function":"Elixir.LoggerJSONTest.test metadata can be configured/1",
    "line":71
  },
  "severity":"DEBUG",
  "time":"2018-10-19T01:10:49.582Z",
  "user_id":13
}

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

{
  "httpRequest":{
    "latency":"0.350s",
    "remoteIp":"::ffff:10.142.0.2",
    "requestMethod":"GET",
    "requestUrl":"http://10.16.0.70/",
    "status":200,
    "userAgent":"kube-probe/1.10+"
  },
  "insertId":"1g64u74fgmqqft",
  "jsonPayload":{
    "log":"",
    "phoenix":{
      "action":"index",
      "controller":"Elixir.MyApp.Web.PageController",
    },
    "request_id":"2lfbl1r3m81c40e5v40004c2",
    "vm":{
      "hostname":"myapp-web-66979fc-vbk4q",
      "pid":1,
    }
  },
  "logName":"projects/hammer-staging/logs/stdout",
  "metadata":{
    "systemLabels":{},
    "userLabels":{}
  },
  "operation":{
    "id":"2lfbl1r3m81c40e5v40004c2"
  },
  "receiveTimestamp":"2018-10-18T14:33:35.515253723Z",
  "resource":{},
  "severity":"INFO",
  "sourceLocation":{
    "file":"iex",
    "function":"Elixir.LoggerJSON.Plug.call/2",
    "line":"36"
  },
  "timestamp":"2018-10-18T14:33:33.263Z"
}

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 and :jason to your list of dependencies in mix.exs:

def deps do
  [{:logger_json, "~> 3.0"}]
end

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

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

3. 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.

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

config :logger,
  backends: [LoggerJSON]

5. Optionally. Log requests and responses by replacing a Plug.Logger in your endpoint with a:

plug LoggerJSON.Plug

6. Optionally. Log Ecto queries via Plug:

config :my_app, MyApp.Repo,
  adapter: Ecto.Adapters.Postgres,
  ...
  loggers: [{LoggerJSON.Ecto, :log, [:info]}]

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, []}

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 https://hexdocs.pm/logger_json

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.