There is not much here other than a base alpine image with packages needed to run openvpn: openssl, easy-rsa, openvpn, and iptables. Much of the configuration is done through kubernetes and helm. Please refer to the scripts here for better understanding.
That chart originally used a base Alpine image, but the Alpine repositories worked inconsistently so this image was created to remove a point of failure.
To rebuild:
git clone https://github.com/jfelten/openvpn-docker.git
cd openvpn-docker
docker build .