An image based on OpenWrt x86_64 which runs an sftp server.
The simplest case is to specify user name and password when starting the container:
docker run -p 11022:22 -it --rm -e SFTP_USER=scott -e SFTP_PASS=tiger mcreations/openwrt-sftp
Now, you can sftp to this docker instance with
sftp -P 11022 scott@localhost