services:
    ...
    Customize\Log\Processor\DoctrineProcessor:
        tags:
            - { name: monolog.processor, channel: doctrine }

class DoctrineProcessor {

    private ManagerRegistry $managerRegistry;

    public function __construct(ManagerRegistry $managerRegistry) {
        $this->managerRegistry = $managerRegistry;
    }

    public function __invoke(array $records) {
        $connect = $this->managerRegistry->getConnection()->isConnectedToMaster() ? 'master' : 'slave';

        $records['message'] = '[' . $connect . ']' . $records['message'];
        return $records;
    }
}