[FR]: Support multi-architecture images build

[farcop]

What is the current behavior?

Now it is unable to use multi-architecture base images in Dockerfile to build multi-architecture images

Describe the feature

I want to build multi-architecture images using rules_buildx.
E.g.

ARCHITECTURES = ["amd64", "arm64"]

[buildx(
    name = "image-installed-utils-{}".format(architecture),
    build_context = [
        context.oci_layout(
            "opensearchproject/opensearch:2.8.0",
            "@opensearch_linux_{}".format(architecture),
            q = "_{}".format(architecture),
        ),
    ],
    dockerfile = ":Dockerfile",
) for architecture in ARCHITECTURES]

Now I use patch with hack for rules_buildx to do so:

diff --git a/buildx/private/buildx_context.bzl b/buildx/private/buildx_context.bzl
index 03c1660..9c19707 100644
--- a/buildx/private/buildx_context.bzl
+++ b/buildx/private/buildx_context.bzl
@@ -47,8 +47,8 @@ oci_layout_buildx_workaround = rule(
     toolchains = ["@aspect_bazel_lib//lib:coreutils_toolchain_type"],
 )
 
-def _context_oci_layout(replace, layout):
-    name = str(replace).replace("/", "_").replace(":", "_")
+def _context_oci_layout(replace, layout, q = ""):
+    name = str(replace).replace("/", "_").replace(":", "_") + q
 
     # TODO: remove once https://github.com/docker/buildx/issues/2753 is solved and set store to layout directly.
     oci_layout_buildx_workaround(

[thesayyn]

This buildx workaround is not needed anymore. We can simply remove it.

[farcop]

@thesayyn Could you please explain how to use buildx() in case when I need to build multiarch image?

[thesayyn]

I have not used it for cross-compiling. Right now its effectively unsupported.

[farcop]

Sorry, I think we had a misunderstanding.
I suspect you mean workaround for this issue docker/buildx#2753 but it is not relevant to this FR.

[arrdem]

It may be feasible to get crossbuilds working via Docker if we either add platform specs to the builder that rules_buildx uses or try to create several single-platform builders which can then be switched between later.