How to Configure Monolog to Email Errors

How to Configure Monolog to Email Errors

Monolog can be configured to send an email when an error occurs with an application. The configuration for this requires a few nested handlers in order to avoid receiving too many emails. This configuration looks complicated at first but each handler is fairly straightforward when it is broken down.

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    # app/config/config_prod.yml
    monolog:
        handlers:
            mail:
                type:         fingers_crossed
                # 500 errors are logged at the critical level
                action_level: critical
                # to also log 400 level errors (but not 404's):
                # action_level: error
                # excluded_404s:
                #     - ^/
                handler:      deduplicated
            deduplicated:
                type:    deduplication
                handler: swift
            swift:
                type:       swift_mailer
                from_email: 'error@example.com'
                to_email:   'error@example.com'
                # or list of recipients
                # to_email:   ['dev1@example.com', 'dev2@example.com', ...]
                subject:    'An Error Occurred! %%message%%'
                level:      debug
                formatter:  monolog.formatter.html
                content_type: text/html
    
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    <!-- app/config/config_prod.xml -->
    <?xml version="1.0" encoding="UTF-8" ?>
    <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 http://symfony.com/schema/dic/services/services-1.0.xsd
                            http://symfony.com/schema/dic/monolog http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
    
        <monolog:config>
            <!--
            500 errors are logged at the critical level,
            to also log 400 level errors (but not 404's):
            action-level="error"
            And add this child inside this monolog:handler
            <monolog:excluded-404>^/</monolog:excluded-404>
            -->
            <monolog:handler
                name="mail"
                type="fingers_crossed"
                action-level="critical"
                handler="deduplicated"
            />
            <monolog:handler
                name="deduplicated"
                type="deduplication"
                handler="swift"
            >
            <monolog:handler
                name="swift"
                type="swift_mailer"
                from-email="error@example.com"
                subject="An Error Occurred! %%message%%"
                level="debug"
                formatter="monolog.formatter.html"
                content-type="text/html">
    
                <monolog:to-email>error@example.com</monolog:to-email>
    
                <!-- or list of recipients -->
                <!--
                <monolog:to-email>dev1@example.com</monolog:to-email>
                <monolog:to-email>dev2@example.com</monolog:to-email>
                ...
                -->
            </monolog:handler>
        </monolog:config>
    </container>
    
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    // app/config/config_prod.php
    $container->loadFromExtension('monolog', array(
        'handlers' => array(
            'mail' => array(
                'type'         => 'fingers_crossed',
                // 500 errors are logged at the critical level
                'action_level' => 'critical',
                // to also log 400 level errors (but not 404's):
                // 'action_level' => 'error',
                // 'excluded_404s' => array(
                //     '^/',
                // ),
                'handler'      => 'deduplicated',
            ),
            'deduplicated' => array(
                'type'    => 'deduplication',
                'handler' => 'swift',
            ),
            'swift' => array(
                'type'         => 'swift_mailer',
                'from_email'   => 'error@example.com',
                'to_email'     => 'error@example.com',
                // or a list of recipients
                // 'to_email'   => array('dev1@example.com', 'dev2@example.com', ...),
                'subject'      => 'An Error Occurred! %%message%%',
                'level'        => 'debug',
                'formatter'    => 'monolog.formatter.html',
                'content_type' => 'text/html',
            ),
        ),
    ));
    

The mail handler is a fingers_crossed handler which means that it is only triggered when the action level, in this case critical is reached. The critical level is only triggered for 5xx HTTP code errors. If this level is reached once, the fingers_crossed handler will log all messages regardless of their level. The handler setting means that the output is then passed onto the deduplicated handler.

Tip

If you want both 400 level and 500 level errors to trigger an email, set the action_level to error instead of critical. See the code above for an example.

The deduplicated handler simply keeps all the messages for a request and then passes them onto the nested handler in one go, but only if the records are unique over a given period of time (60 seconds by default). If the records are duplicates they are simply discarded. Adding this handler reduces the amount of notifications to a manageable level, specially in critical failure scenarios.

The messages are then passed to the swift handler. This is the handler that actually deals with emailing you the error. The settings for this are straightforward, the to and from addresses, the formatter, the content type and the subject.

You can combine these handlers with other handlers so that the errors still get logged on the server as well as the emails being sent:

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    # app/config/config_prod.yml
    monolog:
        handlers:
            main:
                type:         fingers_crossed
                action_level: critical
                handler:      grouped
            grouped:
                type:    group
                members: [streamed, deduplicated]
            streamed:
                type:  stream
                path:  '%kernel.logs_dir%/%kernel.environment%.log'
                level: debug
            deduplicated:
                type:    deduplication
                handler: swift
            swift:
                type:       swift_mailer
                from_email: 'error@example.com'
                to_email:   'error@example.com'
                subject:    'An Error Occurred! %%message%%'
                level:      debug
                formatter:  monolog.formatter.html
                content_type: text/html
    
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    <!-- app/config/config_prod.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 http://symfony.com/schema/dic/services/services-1.0.xsd
                            http://symfony.com/schema/dic/monolog http://symfony.com/schema/dic/monolog/monolog-1.0.xsd">
    
        <monolog:config>
            <monolog:handler
                name="main"
                type="fingers_crossed"
                action_level="critical"
                handler="grouped"
            />
            <monolog:handler
                name="grouped"
                type="group"
            >
                <member type="stream"/>
                <member type="deduplicated"/>
            </monolog:handler>
            <monolog:handler
                name="stream"
                path="%kernel.logs_dir%/%kernel.environment%.log"
                level="debug"
            />
            <monolog:handler
                name="deduplicated"
                type="deduplication"
                handler="swift"
            />
            <monolog:handler
                name="swift"
                type="swift_mailer"
                from-email="error@example.com"
                subject="An Error Occurred! %%message%%"
                level="debug"
                formatter="monolog.formatter.html"
                content-type="text/html">
    
                <monolog:to-email>error@example.com</monolog:to-email>
    
                <!-- or list of recipients -->
                <!--
                <monolog:to-email>dev1@example.com</monolog:to-email>
                <monolog:to-email>dev2@example.com</monolog:to-email>
                ...
                -->
            </monolog:handler>
        </monolog:config>
    </container>
    
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    // app/config/config_prod.php
    $container->loadFromExtension('monolog', array(
        'handlers' => array(
            'main' => array(
                'type'         => 'fingers_crossed',
                'action_level' => 'critical',
                'handler'      => 'grouped',
            ),
            'grouped' => array(
                'type'    => 'group',
                'members' => array('streamed', 'deduplicated'),
            ),
            'streamed'  => array(
                'type'  => 'stream',
                'path'  => '%kernel.logs_dir%/%kernel.environment%.log',
                'level' => 'debug',
            ),
            'deduplicated' => array(
                'type'     => 'deduplication',
                'handler'  => 'swift',
            ),
            'swift' => array(
                'type'         => 'swift_mailer',
                'from_email'   => 'error@example.com',
                'to_email'     => 'error@example.com',
                // or a list of recipients
                // 'to_email'   => array('dev1@example.com', 'dev2@example.com', ...),
                'subject'      => 'An Error Occurred! %%message%%',
                'level'        => 'debug',
                'formatter'    => 'monolog.formatter.html',
                'content_type' => 'text/html',
            ),
        ),
    ));
    

This uses the group handler to send the messages to the two group members, the deduplicated and the stream handlers. The messages will now be both written to the log file and emailed.

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