How to Configure Monolog to Exclude 404 Errors from the Log

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Sometimes your logs become flooded with unwanted 404 HTTP errors, for example, when an attacker scans your app for some well-known application paths (e.g. `/phpmyadmin`). When using a fingers_crossed handler, you can exclude logging these 404 errors based on a regular expression in the MonologBundle configuration:

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        # app/config/config.yml
monolog:
    handlers:
        main:
            # ...
            type: fingers_crossed
            handler: ...
            excluded_404s:
                - ^/phpmyadmin
    

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        <!-- app/config/config.xml -->
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:monolog="http://symfony.com/schema/dic/monolog"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/monolog
        https://symfony.com/schema/dic/monolog/monolog-1.0.xsd">

    <monolog:config>
        <monolog:handler type="fingers_crossed" name="main" handler="...">
            <!-- ... -->
            <monolog:excluded-404>^/phpmyadmin</monolog:excluded-404>
        </monolog:handler>
    </monolog:config>
</container>
    

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        // app/config/config.php
$container->loadFromExtension('monolog', [
    'handlers' => [
        'main' => [
            // ...
            'type'          => 'fingers_crossed',
            'handler'       => ...,
            'excluded_404s' => [
                '^/phpmyadmin',
            ],
        ],
    ],
]);
    

Caution

Combining excluded_404s with a passthru_level lower than error (i.e. debug, info, notice or warning) will not actually exclude log messages for the URL(s) listed in excluded_404s because they are logged with level of error or higher and passthru_level takes precedence over the URLs being listed in excluded_404s.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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