Put your TEMPLATE_NAME blend under version control or choose someone else's.

GITLAB_URL TEMPLATE_NAME BLEND_NAME are ARGS that can be passed to 'docker build', the passwords should be managed via ssh-agent

NB. You might need docker 19.03 or above with
	i.	{ "features": { "buildkit": true } } in /etc/docker/daemon.json
	ii.	# syntax = docker/dockerfile:1.1-experimental at the top of your Dockerfile
	iii.	RUN --mount=type=ssh before any command needing a password 

See https://docs.docker.com/develop/develop-images/build_enhancements/

Installing with 020_docker.sh will install from docker sources.list and configure these features.

 $ docker build --build-arg GITLAB_URL=git.devuan.org TEMPLATE_NAME=devuan-beowulf-live-e17 BLEND_NAME=live-zfs-e17

Change the URL for the submodules:
i.	TEMPLATE_NAME	the blend to base the new blend on.			DEFAULT devuan-beowulf-live-e17
ii.	BLEND_NAME	the new unique blend to create.				DEFAULT live-zfs-e17
iii.	GITLAB_URL	the repo address for the template and the new blend 	DEFAULT git.devuan.org