magento2-custom-logger

name	magento2-custom-logger
description	Custom per-class log files in Magento 2 using di.xml virtual types — no PHP class needed. Use when the user says "custom logger", "dedicated log file", "separate log file", "log to my own file", "virtual type logger", or wants a Console Command / Service to write to a specific var/log/ path. DO NOT use for general Magento logging via \Psr\Log\LoggerInterface already injected by the framework, or for frontend/JS logging.
metadata	{"author":"tuanhaviet22","version":"1.0.0","tags":["magento2","logger","monolog","di.xml","virtual-type","console-command"],"compatibility":"Magento 2.4+, PHP 8.1+"}

Magento 2 Custom Logger via di.xml Virtual Types

Give any class its own dedicated log file without creating a real PHP Logger class — everything is wired through XML virtual types.

---

How it works

Magento's DI container supports virtual types: named aliases for existing classes with different constructor arguments. Two virtual types are needed:

1. Handler — extends Magento\Framework\Logger\Handler\Base, sets fileName
2. Logger — extends Magento\Framework\Logger\Monolog, references the handler

---

etc/di.xml snippet

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">

    <!-- 1. Handler: points to the log file -->
    <virtualType name="Vendor\Module\Logger\Handler\MyFeature"
                 type="Magento\Framework\Logger\Handler\Base">
        <arguments>
            <argument name="fileName" xsi:type="string">/var/log/my_feature.log</argument>
        </arguments>
    </virtualType>

    <!-- 2. Logger: named Monolog channel wrapping the handler -->
    <virtualType name="Vendor\Module\Logger\MyFeatureLogger"
                 type="Magento\Framework\Logger\Monolog">
        <arguments>
            <argument name="name" xsi:type="string">my_feature</argument>
            <argument name="handlers" xsi:type="array">
                <item name="debug" xsi:type="object">Vendor\Module\Logger\Handler\MyFeature</item>
            </argument>
        </arguments>
    </virtualType>

    <!-- 3. Inject into target class -->
    <type name="Vendor\Module\Console\Command\MyCommand">
        <arguments>
            <argument name="logger" xsi:type="object">Vendor\Module\Logger\MyFeatureLogger</argument>
        </arguments>
    </type>

</config>

---

PHP class — constructor injection

Declare LoggerInterface in the constructor; DI injects the virtual logger automatically.

use Psr\Log\LoggerInterface;
use Magento\Framework\App\ResourceConnection;

public function __construct(
    ResourceConnection $resource,
    LoggerInterface $logger,
    ?string $name = null         // only for Console Commands
) {
    $this->resource = $resource;
    $this->logger   = $logger;
    parent::__construct($name);  // only for Console Commands
}

No import of a concrete logger class — always type-hint against Psr\Log\LoggerInterface.

---

Naming conventions

Part	Convention	Example
Handler virtual type	Vendor\Module\Logger\Handler\{Feature}	Distriartisan\Migration\Logger\Handler\FixData
Logger virtual type	Vendor\Module\Logger\{Feature}Logger	Distriartisan\Migration\Logger\FixDataLogger
Monolog channel name	dot-separated, lowercase	migrate.fix_data
Log file path	/var/log/{context}/{feature}.log	/var/log/migrate/fix_data.log

---

Rules

• fileName is relative to {MAGENTO_ROOT} — the leading /var/log/ maps to {MAGENTO_ROOT}/var/log/.
• The handlers array item key (debug) sets the minimum log level captured; debug captures everything. Use info, warning, or error to filter.
• One Handler + one Logger virtual type pair per log file destination.
• Virtual type names must be globally unique — namespace them under your module.
• Never inject a concrete logger class directly; always use Psr\Log\LoggerInterface in the PHP constructor.
• Works for any injectable class: Console Commands, Services, Observers, Plugins, etc.
• After adding or modifying di.xml, run bin/magento setup:di:compile (or bin/magento cache:flush in developer mode).