title: How to change Monolog channel for some controllers Symfony 3.4 or 4+
body: <p>I want to change Monolog channel. My declarations works with some classes but never with controllers.</p>
  
  <p>Here is my new <em>admin</em> channel declaration:</p>
  
  <pre><code>#config/packages/dev/monolog.yaml
  monolog:
      handlers:
          admin:
              type: stream
              path: "%kernel.logs_dir%/%kernel.environment%-admin.log"
              level: debug
              channels: ["admin"]
  </code></pre>
  
  <p>I use it successfuly with my Authenticator by adding a tag:</p>
  
  <pre><code>#config/services.yaml
  # The form guard authenticator for the admin access
  app.security.admin_authenticator:
      class: App\Security\AdminAuthenticator
      autowire: true
      tags:
          - { name: monolog.logger, channel: admin}
  </code></pre>
  
  <p>The last line of <code>services.yaml</code> file do the job, my Authenticator is no more logging in <em>app</em> channel, it's logging in <em>admin</em> channel.</p>
  
  <p>Now, I want to use this channel with the controllers under the Admin subdirectory, so I add a similar tag in my declaration:</p>
  
  <pre><code>#config/services.yaml
  App\Controller\Admin\:
      resource: '../src/Controller/Admin'
      tags:
          - 'controller.service_arguments'
          - { name: monolog.logger, channel: admin}
  </code></pre>
  
  <p>But it seems there is no impact. I am still logging in <em>app</em> channel.
  (I did some verification, like refresh the cache). I don't find my error.</p>