Mount S3 Bucket on AWS ECS
Consider that S3 is a storage platform with very specific characteristics; it doesn't allow for partial update, it doesn't actually has a folder structure and so on. On the surface it might have a lot of similarities with a filesystem, but it is not build to be one nor should it be used as one.
You can create and attach EBS or EFS volumes to your Docker container. Alternatively, you could use or create a plugin that stores some data on S3 with the specific API's that S3 has.
You can install s3fs in your EC2 instances (or may be use a custom AMI for your ECS cluster). Mount the S3 bucket in the EC2 instance and then you can always share the host path.