Add example of building a Dockerfile with local tar file build context

[njlr]

This PR adds an example of using a Dockerfile with a local tar as a build context.

This is not the ideal approach, which this is clearly signposted in the README!, but it shows an easy migration path from rules_docker. The existing example does not show how Bazel build artefacts can be passed to BuildX.

How it works:

1. Create a tar file using rules_pkg
2. Pipe the tar file into BuildX using sh_binary and run_binary
3. Use the BuildX output as a base for an oci_image

This is a replacement for container_run_and_commit.

The example could easily be adapted to behave like container_run_and_extract by changing the --output flag to a tar.

[thesayyn]

We have https://github.com/bazel-contrib/rules_oci/tree/main/examples/dockerfile, how is this different than that one?

[njlr]

We have https://github.com/bazel-contrib/rules_oci/tree/main/examples/dockerfile, how is this different than that one?

That example does not show how to use the output of other Bazel targets as input to the Dockerfile build

[thesayyn]

That example does not show how to use the output of other Bazel targets as input to the Dockerfile build

Than can we change it so it does? i don't see the difference between this example and the other one, other than putting the srcs into a tar file beforehand so you don't have to deal with paths that start with bazel-bin/cfg/bin

[njlr]

That example does not show how to use the output of other Bazel targets as input to the Dockerfile build

Than can we change it so it does? i don't see the difference between this example and the other one, other than putting the srcs into a tar file beforehand so you don't have to deal with paths that start with bazel-bin/cfg/bin

Yes, happy to do this.

The reason I made a new example is that it's a little more complicated than the existing example, so might hinder understanding.

What do you think?

[thesayyn]

We can add some comments explaining why there is two different buildx targets in the same package and the difference.

[njlr]

We can add some comments explaining why there is two different buildx targets in the same package and the difference.

I have merged the two examples

[thesayyn]

thanks!

[thesayyn]

actually can we not use pkg_tar here? we have bazel-lib dependency here already. you can use https://github.com/bazel-contrib/bazel-lib/blob/main/docs/tar.md

(i don't want a pkg_tar dependency even if it's dev_dep)

[njlr]

I might need some assistance with this one.

When I try bazel build //examples/dockerfile:buildx_context I get:

tar: Unrecognized archive format
tar: Error exit delayed from previous errors.
Target //examples/dockerfile:buildx_context failed to build

Any ideas?

[thesayyn]

There are some failures, can you take a look?