When creating a buildpack with docker buildx --platform linux/arm64 pack does not set the architecture

[jericop]

Summary

The following occurs when running pack from a dockerfile using docker buildx build. When creating a buildpack with pack buildpack package the architecture is always an empty string, regardless of the architecture you run on.

This issue is similar to #1958, except that it affects pack buildpack package instead of pack builder create.

Reproduction

Note that docker needs to be configured to build multi-arch images for this to work as described here.

Steps

1. Create the following dockerfile in a directory.

FROM buildpacksio/pack as pack

FROM bitnami/git
USER root
WORKDIR /workspace

COPY --from=pack /usr/local/bin/pack /usr/local/bin/pack

RUN <<RUN_EOF

image_arch=amd64
if [ $(arch) = "aarch64" ]; then
  image_arch=arm64
fi

git clone --depth 1 --branch main https://github.com/buildpacks/samples.git

pack buildpack package ttl.sh/jericop-hello-world-buildpack:${image_arch} --publish \
  --path samples/buildpacks/hello-world

RUN_EOF

2. Run the following docker buildx command to create and publish buildpacks to ttl.sh, an ephemeral registry.

docker buildx build --platform linux/amd64,linux/arm64 .

3. Inspect the image config with crane to confirm the architecture is an empty string.

➜  pack-arch-issue crane ls ttl.sh/jericop-hello-world-buildpack
amd64
arm64
➜  pack-arch-issue crane config ttl.sh/jericop-hello-world-buildpack:amd64 | jq .architecture
""
➜  pack-arch-issue crane config ttl.sh/jericop-hello-world-buildpack:arm64 | jq .architecture
""
➜  pack-arch-issue 

Current behavior

The architecture is empty, which prevents building multi-arch images without modifying the image or doing some docker manifest magic.

Expected behavior

The architecture should match the architecture that pack is running on.

---

Environment

pack info

Pack:
  Version:  0.33.2+git-f2cffc4.build-5562
  OS/Arch:  darwin/amd64

Default Lifecycle Version:  0.18.5

Supported Platform APIs:  0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.10, 0.11, 0.12

docker info

Client:
 Version:    25.0.3
Server:
 Server Version: 25.0.3

[jericop]

I believe this change also addresses #1968, which was fixed by adding retry logic.

[WYGIN]

I will take this issue, as I already did some changes in imgutil related to it :)

[jericop]

@WYGIN I have a pull request with changes and unit tests already here. Maybe we can figure out how to merge the changes together.

[jjbustamante]

@jericop

We are working to include #2086 into pack 0.34.0 that PR should fix this issue! I think we can close #2080 in favor on that one.

[jjbustamante]

With the implementation of RFC 0128 you don't need to use docker buildx to create a multi-platform buildpack package.

From your Dockerfile configuration, you just need to do is:

pack buildpack package ttl.sh/jericop-hello-world-buildpack:${image_arch} --publish \
  --path samples/buildpacks/hello-world \
  --target linux/amd64 \
  --target linux/arm64 

and pack will create the manifests with the correct os and architecture.

Using the binary from the open PR I did this:

> $PACK_BINARY buildpack package ttl.sh/jjbustamante-hello-world-buildpack:${image_arch} --publish --path samples/buildpacks/hello-world --targe
t linux/amd64 --target linux/arm64
Successfully pushed manifest list ttl.sh/jjbustamante-hello-world-buildpack: to registry
Successfully published package ttl.sh/jjbustamante-hello-world-buildpack: and saved to registry

# Inspect the Index
> crane manifest  ttl.sh/jjbustamante-hello-world-buildpack | jq .
{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.index.v1+json",
  "manifests": [
    {
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 402,
      "digest": "sha256:46ee213ae13e9e33a486f95780bdd09cda71955bcb55d4ceffe423265c752e3f",
      "platform": {
        "architecture": "amd64",
        "os": "linux"
      }
    },
    {
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 402,
      "digest": "sha256:11d69032ed77c74be777d081321af19617fb1acd660f02b01f7ec46b85481130",
      "platform": {
        "architecture": "arm64",
        "os": "linux"
      }
    }
  ]
}

# Inspecting each digest

> crane config ttl.sh/jjbustamante-hello-world-buildpack@sha256:11d69032ed77c74be777d081321af19617fb1acd660f02b01f7ec46b85481130 | jq .architecture
"arm64"

> crane config ttl.sh/jjbustamante-hello-world-buildpack@sha256:46ee213ae13e9e33a486f95780bdd09cda71955bcb55d4ceffe423265c752e3f | jq .architecture
"amd64

I think this is the expected output, right? docker buildx was used to deal with the Image Index creation 😄