!UPDATE! docker-debian-sftp now has support for other architectures

docker-debian-sftp has support for: amd64, i386, arm64 and armv7.
Filestash still only has support for amd64 (not up to me, because it's not my project). If you work on arm port of Filestash, please let me know.

GitHub: https://github.com/Cimlah/docker-debian-sftp
DockerHub: https://hub.docker.com/repository/docker/cimlah/docker-debian-sftp

Docker-debian-sftp is a Docker container running sftp server. Not only you get isolation from the side of Docker, but also there is chroot in sshd_config set-up.
It is meant to run alongside with Filestash, but can very simply edit docker-compose.yml not to use Filestash.

First of all, choose proper docker-compose.yml file for your architecture (either docker-compose_amd64.yml or docker-compose_other-architectures.yml) and rename it to docker-compose.yml.
While in main directory of this repo, you can simply execute command: docker-compose up -d or copy content of my docker-compose.yml:

version: '3.3'

services:
    debian-sftp:
        image: cimlah/docker-debian-sftp:latest
        restart: unless-stopped
        hostname: debian-sftp
        container_name: debian-sftp
        ports:
            - "2800:22"
        stdin_open: true
        tty: true
        volumes: 
            - /path/you/want/to/use:/home

    filestash:
        image: machines/filestash
        restart: unless-stopped
        hostname: filestash
        container_name: filestash
        ports:
            - "8334:8334"
        environment: 
            - APPLICATION_URL=
            - GDRIVE_CLIENT_ID=<gdrive_client>
            - GDRIVE_CLIENT_SECRET=<gdrive_secret>
            - DROPBOX_CLIENT_ID=<dropbox_key>
            - ONLYOFFICE_URL=http://onlyoffice

If you don't want to use Filestash just delete lines of code associated with filestash service or copy:

version: '3.3'

services:
    debian-sftp:
        image: cimlah/docker-debian-sftp:latest
        restart: unless-stopped
        hostname: debian-sftp
        container_name: debian-sftp
        ports:
            - "2800:22"
        stdin_open: true
        tty: true
        volumes: 
            - /path/you/want/to/use:/home

Remember to change line: - /path/you/want/to/use:/home, so the files from debian-sftp container get mounted in a place you want. It is good to mount in case something happens to container, if so you still have access to all files located in this container.

I wrote a simple script called user_add.sh, which creates users and sets proper permission for their files.
If you want to use it, you can execute command from your host OS: docker exec -it debian-sftp user_add, write user name and password when asked to do so. Another way is to get inside container (e. g. docker exec -it debian-sftp bash) and there execute user_add.
Please, read my script to know what permissions are set by it.

Of course, if you want to change something, for example in sshd_config, do it and then build the image yourself. In directory build_it_yourself you have everything needed to customise and build the image.
To build the image, execute command: docker build -t *name of your image* . while you're inside build_it_yourself directory.