Log

    'components' => [
        'log' => [
            'traceLevel' => YII_DEBUG ? 3 : 0,
            'targets' => [
                [
                    'class' => 'yii\log\FileTarget',
                    'levels' => ['error', 'warning'],
                ],
            ],
        ],
    ],

• yii\log\FileTarget
• yii\log\DbTarget
• yii\log\EmailTarget
• yii\log\SyslogTarget