Symfony, Monolog and different log types

Symfony uses the excellent Monolog library for logging everything related to the symfony application stack. But sometimes you need a different logger that responds differently to the log error levels. Ideally you don’t want to reuse the application log mechanism to avoid messing with the fingers crossed listener of Monolog, that keeps the application log files small in case no errors occur.

This can be easily done with Symfonys MonologBundle with a feature called channel. Every log handler, such as file, syslog, mail or fingers crossed is attached to the default logger called “app”. This is referenced by the dependency injection service called monolog.logger.

If you want to create a different logger service that is responsible for a different type of your application stack, just define it using the channels option:

monolog:
    handlers:
        myfile:
            type: stream
            path: %kernel.logs_dir%/myfile.log
            channels: mychannel

To actually write to mychannel you have to tag all the services that use mychannel with the following tag:

<service id="my_service" class="MyService">
    <tag name="monolog.logger" channel="mychannel" />
    <argument type="service" id="logger" />
</service>

With this approach you are now as flexible as with the default channel app regarding to logging in development, testing and production environments for example. Once there is a channel created through the DIC tag, you can actually fetch it from the DIC with monolog.logger.mychannel in our example. I don’t like this approach too much, because it misuses tags for modifying arguments, where tags are actually for the services themselves. However it is usable and works.

This feature is included starting with Symfony 2.1. It is documented in a cookbook entry, however some insights of this blog post are still inside a pending Pull Request.

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