Where did the built multi-platform image go?

[Rory-Z]

I really like buildx, I want to use it in my code, but I have a issue.
I executed the docker buildx build --platform=linux/amd64,linux/386 -f . --output=type=image command and output the following information.

 => exporting to image                                                                                                                                                                                          0.1s
 => => exporting layers                                                                                                                                                                                         0.0s
 => => exporting manifest sha256:f70f46db5ab5126060072198f9fe4056240cf5ab9f0819a60bc141501d5b1198                                                                                                               0.0s
 => => exporting config sha256:af6012ceb069e31c852bb3e509eaab5cfdc1fca82d336e1a014cc7672989bcf6                                                                                                                 0.0s
 => => exporting manifest sha256:b71684386f12acf835cf00fe1c1de7be104535d6debca08cf7789430c1d53456                                                                                                               0.0s
 => => exporting config sha256:0847da7ba34f27312e9e16eb015a309b290322c5d99ee64d56a172a75c906423                                                                                                                 0.0s
 => => exporting manifest list sha256:4eb73fed7ba678c004b851cefcf2c8d9e5b60ce8bfceb3df09f32c08fbdd0296                                                                                                          0.0s

But I can't find my image. Where did it go?

[tonistiigi]

Add push=true to the output or use --output type=registry to push the image to registry during build to access it.

[Rory-Z]

@tonistiigi For some reason I don't want to push the image to the registry. Is there any other way?

[tonistiigi]

There are other outputs as well. https://github.com/docker/buildx#-o---outputpath-typetypekeyvalue I pointed you to registry because you are building a multi-platform image, therefore I assumed you need to distribute it to multiple machines.

[Rory-Z]

@tonistiigi I tried to use --output=tar, but it outputs a directory structure instead of a tarball. What should I do?

$ tree tar -L 2
tar
├── linux_386
│   ├── bin
│   ├── dev
│   ├── etc
│   ├── home
│   ├── lib
│   ├── media
│   ├── mnt
│   ├── opt
│   ├── proc
│   ├── root
│   ├── run
│   ├── sbin
│   ├── srv
│   ├── sys
│   ├── tmp
│   ├── usr
│   └── var
└── linux_amd64
    ├── bin
    ├── dev
    ├── etc
    ├── home
    ├── lib
    ├── media
    ├── mnt
    ├── opt
    ├── proc
    ├── root
    ├── run
    ├── sbin
    ├── srv
    ├── sys
    ├── tmp
    ├── usr
    └── var

[tonistiigi]

What way do you wish to access the image?

[Rory-Z]

I want to be able to access multi-platform built-in images directly in the docker images. If not, I want to be able to export the image to a file, similar to the work of docker save. I guess --output = tar is equivalent to docker build && docker save, is that the case?

[tonistiigi]

Docker does not support multi-platform images locally atm. Local image extracted in docker can only be for a single platform that the current node is based on. --output type=oci gives you the oci transport tarball with layers for all subimages.

[tonistiigi]

I guess --output = tar is equivalent to docker build && docker save, is that the case?

No, that would be --output type=docker (with the limitations listed above)

[Rory-Z]

I use --output=oci , but I don't see how it differs from --output=tar

$ tree oci/ -L 2
oci/
├── linux_386
│   ├── bin
│   ├── dev
│   ├── etc
│   ├── home
│   ├── lib
│   ├── media
│   ├── mnt
│   ├── opt
│   ├── proc
│   ├── root
│   ├── run
│   ├── sbin
│   ├── srv
│   ├── sys
│   ├── tmp
│   ├── usr
│   └── var
└── linux_amd64
    ├── bin
    ├── dev
    ├── etc
    ├── home
    ├── lib
    ├── media
    ├── mnt
    ├── opt
    ├── proc
    ├── root
    ├── run
    ├── sbin
    ├── srv
    ├── sys
    ├── tmp
    ├── usr
    └── var

[tonistiigi]

Post full commands of what you are running.

[Rory-Z]

docker buildx build --platform=linux/amd64,linux/386 -t emqx/emqx:test -f deploy/docker/Dockerfile . --output=oci

[tonistiigi]

--output type=oci https://github.com/docker/buildx#-o---outputpath-typetypekeyvalue

[wohali]

Hi @tonistiigi , I'm having the same issue, and may be trying to solve the same problem as @zhanghongtong .

Our goal is to export each of the separate built images locally to the docker daemon, and validate them locally (using https://github.com/multiarch/qemu-user-static and various test cases) before pushing them to the registry.

With --output type=oci I'm getting:

failed to solve: rpc error: code = Unknown desc = oci exporter cannot export named image

Is this possible at all without this kind of approach (given our Dockerfile is under a subdirectory named $VERSION):

for ARCH in amd64 arm64v8 ppc64le; do
  from="$(awk '$1 == toupper("FROM") { print $2 }' $VERSION/Dockerfile)"
  docker pull "$ARCH/$from"
  docker tag "$ARCH/$from" "$from"
  docker build -t apache/couchdb:$arch-$VERSION $VERSION
done

allowing access to each separate platform image as apache/couchdb:$arch-$version locally for validation, then assembling the manifest and pushing later?

Building all of the images at once, and bringing them over one at a time for testing would be acceptable, too.