Use Dockerfile ARGs

[berney]

Use Dockerfile ARGs

[r7l]

I am not against this change but i'd guess this change would break any existing image as you would have to replace all the template files with a Dockerfile. I actually prefer the current name as it makes clear that it's not a simple Dockerfile on it's own but instead it's a template that will be used and maybe even altered by Kubler.

[berney]

Thanks for the comments r71.

I working on #215 and was thinking it could simplify kubler, by leveraging docker features.

Right now I mostly see IMAGE_PARENT and MAINTAINER like the figlet example in the OP. The MAINTAINER seems to be just a way to centralise it, in your central kubler.conf you can update this, and every image will get the update.

The IMAGE_PARENT is important as it is used to define the dependency graph hierarchy, if build.conf didn't declare it and it was just hardcoded in the FROM directives then kubler wouldn't understand the image dependency graph, couldn't order the builds, and dependency images would be missing due to not being built yet.

[r7l]

Maybe i got your idea wrong. What i meant is that currently every image has a file called Dockerfile.template like you've said and the .template file extension is a nice way to not mix this template file with a real Dockerfile.

I don't mind changing these variables if this helps. But it's up to @edannenberg anyways.

[berney]

You understood me right. I was thinking to effectively git mv Dockerfile.template Dockerfile, and to add the ARG IMAGE_PARENT etc to the dockerfile, and then in the docker build commands add the --build-arg IMAGE_PARENT="${IMAGE_PARENT}" sort of thing.

The way Kubler is right now, before a build, you have the Dockerfile.template, and after a build you have the generated Dockerfile with the concrete values, and the rootfs.tar, together which is enough to feed to native docker to (re)create the image.