oneup_flysystem:
    adapters:
        aws_s3_adapter:
            awss3v3:
                client: aws.s3_client
                bucket: '%env(AWS_S3_BUCKET)%'
                prefix: '%env(DATABASE_NAME)%'

# define the ez handlers
ez_io:
    binarydata_handlers:
        aws_s3:
            flysystem:
                adapter: aws_s3_adapter
    metadata_handlers:
        dfs:
            legacy_dfs_cluster:
                connection: doctrine.dbal.default_connection

...

ezplatform:
    system:
        default:
            io:
                binarydata_handler: aws_s3
                metadata_handler: dfs
                url_prefix: '%env(AWS_BASE_URL)%'

services:
    aws.s3_client:
       class: Aws\S3\S3Client
       arguments:
           - version: '2006-03-01' 
             region: "eu-central-1" # 'eu-central-1' for example
             credentials:
                 key: "aws-key"
                 secret: "aws-secret-key"