Tao platform logger is set in config generis/log.conf.php. It accepts a Psr3 logger interface.

To make life easier a wrapper exists to send log through monolog.

1°) Propagation

The logger is passed to object in platform bootstrapping. It means that ConfigurableService, Action and Controller using LoggerAwareInterface will receive the logger. It can be accessed also via ServiceManager with key generis/log

2°) Log Level

To implements different strategy, developers must use logger following log level described by RFC 5424.

 - **DEBUG** (100): Detailed debug information.

 - **INFO** (200): Interesting events. Examples: User logs in, SQL logs.

 - **NOTICE** (250): Normal but significant events.

 - **WARNING** (300): Exceptional occurrences that are not errors. Examples:
   Use of deprecated APIs, poor use of an API, undesirable things that are not
   necessarily wrong.

 - **ERROR** (400): Runtime errors that do not require immediate action but
   should typically be logged and monitored.

 - **CRITICAL** (500): Critical conditions. Example: Application component
   unavailable, unexpected exception.

 - **ALERT** (550): Action must be taken immediately. Example: Entire website
   down, database unavailable, etc. This should trigger the SMS alerts and wake
   you up.

 - **EMERGENCY** (600): Emergency: system is unusable.

The LoggerAwareTrait provides wrapper methods, see \Psr\Log\LoggerTrait

3°) Tao Monolog

To send log to monolog a wrapper exists: TaoMonolog. It is a configurable service in charge to build the monolog logger from a config.
All monolog handlers can be loaded through taoMonolog. An handler is an array with class to construct and options as constructor arguments.

Example of generis/log config:

return new oat\oatbox\log\LoggerService(array(
       'logger' => array(
           'class' => 'oat\\oatbox\\log\\logger\\TaoMonolog',
           'options' => array(
               'name' => 'tao',
               'handlers' => array(
                   array(
                       'class' => 'Monolog\\Handler\\StreamHandler',
                       'options' => array(
                           '/var/www/tao/package-tao/test-log.log',
                           100
                       )
                   ),
               )
           )
       )
   ));

To have a better view of monolog possibility, please check:

4°) Backward compatibility

To ensure backward compatibility common_Logger wrap all cal to logger service. common_Logger is now deprecated.

To keep logger backward compatibility a TaoLog logger can use old parameter format:

return new oat\oatbox\log\LoggerService(array(
    'logger' => array(
        'class' => 'oat\\oatbox\\log\\logger\\TaoLog',
        'options' => array(
            'appenders' => array(
                //Example of a UDP Appender
                array(
                    'class' => 'UDPAppender',
                    'host' => '127.0.0.1',
                    'port' => 5775,
                    'threshold' => 1,
                    'prefix' => 'tao'
                ),
            )
        )
    ))
));

5°) Using setup.json

To use TaoMonolog:

{
  "generis": {
    "log" : {
      "type": "configurableService",
      "class":"oat\\oatbox\\log\\LoggerService",
      "options": {
        "logger": {
          "class": "oat\\oatbox\\log\\logger\\TaoMonolog",
          "options": {
            "name": "tao",
            "handlers": [
              {
                "class": "Monolog\\Handler\\StreamHandler",
                "options": [
                    "/var/www/tao/package-tao/test-log.log",
                    100
                ]
              },
              {
                "class": "Monolog\\Handler\\BrowserConsoleHandler",
                "options": [
                    200
                ]
              },
              {
                "class": "Monolog\\Handler\\SlackWebhookHandler",
                "options": [
                    "https://hooks.slack.com/services/XXXXXX/XXXXXX/XXXXXX",
                    "#test",
                    "tao-bot"
                ]
              },
              {
                "class": "Monolog\\Handler\\SyslogUdpHandler",
                "options": [
                    "127.0.0.1",
                    "5775"
                ],
                "processors": [
                    {
                      "class": "oat\\oatbox\\log\\logger\\processor\\BacktraceProcessor",
                      "options": [
                        300
                      ]
                    },
                    {
                      "class": "Monolog\\Processor\\MemoryUsageProcessor"
                    },
                    {
                       "class": "Monolog\\Processor\\MemoryPeakUsageProcessor"
                    }
                ]
              }
            ],
            "processors": [
                {
                    "class": "Monolog\\Processor\\PsrLogMessageProcessor"
                },
                {
                    "class": "Monolog\\Processor\\UidProcessor",
                    "options": [
                      24
                    ]
                }
            ]
        }
    }
}

6°) Fluentd Logger

To use Fluentd as log handler combined with trace and environment processors and TAO JSON formatter.

<?php

return new oat\oatbox\log\LoggerService(array(
    'logger' => array(
        'class' => 'oat\\oatbox\\log\\logger\\TaoMonolog',
        'options' => array(
            'name' => 'tao',
            'handlers' => array(
                array(
                    'class' => \oat\oatbox\log\logger\handler\FluentdHandler::class,
                    'options' => [
                        new \Fluent\Logger\FluentLogger(
                            \Fluent\Logger\FluentLogger::DEFAULT_ADDRESS,
                            \Fluent\Logger\FluentLogger::DEFAULT_LISTEN_PORT
                        )
                    ],
                    'processors' => array(
                        array(
                            'class' => \oat\oatbox\log\logger\processor\EnvironmentProcessor::class,
                            'options' => array(
                                100, // Monolog level e.q. debug
                            )
                        ),
                        array(
                            'class' => \oat\oatbox\log\logger\processor\BacktraceProcessor::class,
                            'options' => array(
                                300, // Monolog level e.q. error
                                true,
                            )
                        )
                    ),
                    'formatter' => array(
                        'class' => \oat\oatbox\log\logger\formatter\TaoJsonLogFormatter::class,
                    ),
                ),
            ),
        )
    )
));

To use the old format:

{
  "log": {
    "type": "configurableService",
    "class":"oat\\oatbox\\log\\LoggerService",
    "options": {
      "logger": {
        "class": "oat\\oatbox\\log\\logger\\TaoLog",
        "options": {
            "appenders": [
                {
                   "class": "UDPAppender",
                   "host": "127.0.0.1",
                   "port": 5775,
                   "threshold": 1,
                   "prefix": "offline"
                }
            ]
        }
      }
    }
  }
}