How to Configure Monolog to Exclude 404 Errors from the Log

How to Configure Monolog to Exclude 404 Errors from the Log

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:

  • YAML
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    # app/config/config.yml
    monolog:
        handlers:
            main:
                # ...
                type: fingers_crossed
                handler: ...
                excluded_404s:
                    - ^/phpmyadmin
    
  • XML
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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>
    
  • PHP
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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.