How to properly back up Docker volumes?

My problem was to develop a backup strategy for a running Linux server with multiple docker containers which used docker volume to store data. The problem was that it’s not trivial to just tar an volume like an bind mount. The recommended way to achieve this is to first launch a new container and mount the volume from the running container. Then to mount an local host directory as e.g. “/backup” and finally to pass a command that tars the contents of the data volume to a backup.tar file inside our “/backup” directory.