public function s3CreatFileAction(Request $request) {

   $filesystem = $this->get('knp_gaufrette.filesystem_map')->get('profile_photos');
   $filesystem->write('test.txt', 'hello world');

   [...]
}

$filesystem = $this->get('knp_gaufrette.filesystem_map')->get('profile_photos');
$file = $filesystem->get('test.txt');

#app/config/config.yml

services:
    acme.aws_s3.client:
        class: AwsS3S3Client
        factory_class: AwsS3S3Client
        factory_method: 'factory'
        arguments:
            -
                key: %amazon_s3.key%
                secret: %amazon_s3.secret%

# knp_gaufrette
knp_gaufrette:
    adapters:
        profile_photos:
            aws_s3:
                service_id: 'acme.aws_s3.client'
                bucket_name: 'myBucket'
                options:
                    directory: 'myDirectory'
                    acl: 'public-read'