I've been using Packer with the Docker post-processor. I’ve had to give up multi-stage builds but being able to ditch Dockerfiles and simply write a shell script without a thousand &&\’s is more than enough reason to keep me using it.
I don't understand your point. If all you want to do is set a container image by running a shell script, why don't you just run the shell script in your Dockerfile?
Or better yet, prepare your artifacts before, and then build the Docker image by just copying your files.
It sounds like you decided to take the scenic route of Docker instead of just taking the happy path.
Meanwhile, I write packer files in HCL - a saner language and a saner format - without worrying about the way files are copied. Of course, it’s not perfect but I’d choose any of the other suggestions here before going back to Dockerfiles based on your optimism and the knowledge - that I already had but virtually every author of a Dockerfile ignores - that I can RUN a script. Thanks, but no thanks.