messenger_bus.yaml

# services.yaml
services:
    _instanceof:
        # Add a tag `app.pre_handler` to all classes that implements App\PreHandlerInterface
        App\PreHandlerInterface:
            tags: [ 'app.pre_handler' ]
        # Add a tag `app.post_handler` to all classes that implements App\PostHandlerInterface    
        App\PostHandlerInterface:
            tags: [ 'app.post_handler' ]
    _defaults:
        autowire: true
        autoconfigure: true
        bind:
            # Bind a variable $preHandlers, it contains an iterator 
            # of all classes with tag app.pre_handler
            # this variables will be injected in `Bus`
            $preHandlers: !tagged_iterator app.pre_handler
            # bind a variable $postHandlers, it contains an iterator 
            # of all classes with tag app.post_handler            
            # this variables will be injected in `Bus`
            $postHandlers: !tagged_iterator app.post_handler