Magento2 Logging – How to Create a Custom Log File

logloggingmagento2

In Magento 1, it was common to segment logs into different files (to separate logs for payment methods, etc.). That's as easy as changing the $file parameter of Mage::log.

Magento 2 has changed to use Monolog.

It appears that Monolog (or Magento2's implementation of it) segments all logs for the entire framework to handlers by severity. There are a few handlers that write to file:

\Magento\Framework\Logger\Handler\Debug, \Magento\Framework\Logger\Handler\Exception, \Magento\Framework\Logger\Handler\System

Logging to respective files in var/log as in Magento 1.

I could add a handler for a particular severity (IE, write notices to var/log/notice.log). Extend \Magento\Framework\Logger\Handler\Base, and register the handler in di.xml.

This article roughly describes that process: http://semaphoresoftware.kinja.com/how-to-create-a-custom-log-in-magento-2-1704130912

But how do I go about writing all logs (not just one severity) for one class (not all of Magento) to my file of choice?

It looks like I'll have to create my own version of Magento\Framework\Logger\Monolog, but then how does everything fit together for that to actually work?

If this is a big no-no in Magento 2, then what is the alternative? I want something to separate the logs for this extension for the purpose of debugging it when necessary on client sites. Having that info written to system.log, exception.log, etc. and jumbled with the logs of every other module is not practical.

Best Answer

You do not need to customize or try to extend Magento2's logging. As you said it's using Monolog with only slight customization. It is sufficient to write your own logger extending Monolog with very little effort.

Assuming your module is in YourNamespace/YourModule:

1) Write Logger class in Logger/Logger.php:

<?php
namespace YourNamespace\YourModule\Logger;

class Logger extends \Monolog\Logger
{
}

2) Write Handler class in Logger/Handler.php:

<?php
namespace YourNamespace\YourModule\Logger;

use Monolog\Logger;

class Handler extends \Magento\Framework\Logger\Handler\Base
{
    /**
     * Logging level
     * @var int
     */
    protected $loggerType = Logger::INFO;

    /**
     * File name
     * @var string
     */
    protected $fileName = '/var/log/myfilename.log';
}

Note: This is the only step that uses the Magento code. \Magento\Framework\Logger\Handler\Base extends Monolog's StreamHandler and e.g. prepends the $fileName attribute with the Magento base path.

3) Register Logger in Dependency Injection etc/di.xml:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="YourNamespace\YourModule\Logger\Handler">
        <arguments>
            <argument name="filesystem" xsi:type="object">Magento\Framework\Filesystem\Driver\File</argument>
        </arguments>
    </type>
    <type name="YourNamespace\YourModule\Logger\Logger">
        <arguments>
            <argument name="name" xsi:type="string">myLoggerName</argument>
            <argument name="handlers"  xsi:type="array">
                <item name="system" xsi:type="object">YourNamespace\YourModule\Logger\Handler</item>
            </argument>
        </arguments>
    </type>
</config>

Note: This is not strictly required but allows the DI to pass specific arguments to the constructor. If you do not do this step, then you need to adjust the constructor to set the handler.

4) Use the logger in your Magento classes:

This is done by Dependency Injection. Below you will find a dummy class which only writes a log entry:

<?php
namespace YourNamespace\YourModule\Model;

class MyModel
{
    /**
     * Logging instance
     * @var \YourNamespace\YourModule\Logger\Logger
     */
    protected $_logger;

    /**
     * Constructor
     * @param \YourNamespace\YourModule\Logger\Logger $logger
     */
    public function __construct(
        \YourNamespace\YourModule\Logger\Logger $logger
    ) {
        $this->_logger = $logger;
    }

    public function doSomething()
    {
        $this->_logger->info('I did something');
    }
}
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