alt Hacker NewsHuh?
Each layer is a tarball.
So build your tarballs (concurrently!), and then add some metadata to make an image.
From your comment elsewhere it seems maybe you are expecting the docker build paradigm of running a container and snapshotting it at various stages.
That is messy and has a number of limitations — not the least of which is cross-compilation. Reproducibility being another. But in any case, that definitely not what these rules are trying to do.
I don't quite understand how it handles running binaries then. For example, I want to do `bash -c "ls -la /"`. How would it run this command? It needs to assemble the filesystem at this point in the build process.
I guess the answer for Bazel is "don't do this"? Docker handles cross-compilation by using emulators, btw.