Huh?

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.

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cyberax 8 hours ago | parent [-]

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.

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paulddraper 6 hours ago | parent [-]

> “don’t do this”

Yes. The Bazel way use to produce binaries, files, directories, and then create an image “directly” from these.

Much as you would create a JAR or ZIP or DEB.

This is (1) fast (2) small and (3) more importantly reproducible. Bazel users want their builds to produce artifacts that are exactly the same, for a number of reasons. Size is also nice…do you really need ls and dozens of other executables in your containerized service?

Most Docker users don’t care about reproducibility. They’ll apt-get install and get one version today and another version tomorrow.

Good? Bad? That’s a value judgement. But Bazel users have fundamentally different objectives.

> emulators

Yeah emulators is the Docker solution for producing images of different architectures.

Since Bazel doesn’t run commands as a running container, it skips that consideration entirely.

	▲	cyberax 4 hours ago \| parent [-]
		> Size is also nice…do you really need ls and dozens of other executables in your containerized service? Yeah, I do. For debugging mostly :( > Most Docker users don’t care about reproducibility. They’ll apt-get install and get one version today and another version tomorrow. Ubuntu has daily snapshots. Not great, but works reasonably well. I tried going down the Nix route, but my team (well, and also myself) struggled with it. I'd love to have fully bit-for-bit reproducible builds, but it's too complicated with the current tooling. Especially for something like mobile iOS apps (blergh).