As docker image already become norm these days, multiplatform image is inevitable. What is multiplatform image? Multiplatform image can be pulled by many systems in single tag, so intead using :someversion-arm64 tag or :someversion-amd64 we can :someversion tag only. Before buildx intoduced there is also some hacky way, to made this happed, lets call it manifest manipulation, in this method image created and pushed separately then manipulating the manifest of docker image tag, making it conjunct/referencing with the image build separately.

Build Flows:

Dockerfile

ARG ARCH=
FROM ${ARCH}debian:latest
RUN apt update && apt install -y python3-minimal && apt clean && rm -rf /var/lib/apt/lists/* && mkdir /data
WORKDIR /data
CMD ["python3","-m","http.server"]

Building the images

$ docker build -t registry-url/application-name:tag-amd64 --build-arg ARCH=amd64/ .
$ docker build -t registry-url/application-name:tag-arm32v7 --build-arg ARCH=arm32v7/ .
$ docker build -t registry-url/application-name:tag-arm64v8 --build-arg ARCH=arm64v8/ .

Pushing the images

$ docker push registry-url/application-name:tag-amd64
$ docker push registry-url/application-name:tag-arm32v7
$ docker push registry-url/appplication-name:tag-arm64v8

Here we had 3 images, with 3 different manifest, then we create a new manifest by using the other images manifest.

Create manifest

$ docker manifest create \
registry-url/application-name:tag-latest \
--amend docker push registry-url/application-name:tag-amd64 \
--amend registry-url/application-name:tag-arm32v7 \
--amend registry-url/appplication-name:tag-arm64v8

Lastly we push the tag-latest manifest, Push manifest

$ docker manifest push registry-url/application-name:tag-latest

The current way is using buildx, by using buildx build docker images become simpler but also need to pay attention few things. In simple terms:

docker run --rm --privileged tonistiigi/binfmt:latest -install all
docker buildx create --name MultiArch
docker buildx use MultiArch
docker buildx build --push --platform linux/amd64,linux/arm64 -t registry-url/application-name:tag-latest .

What exactly happen?

1. We run docker images that emulates multiarch
2. Create to builder container named MultiArch
3. Tell buildx use builder container named MultiArch
4. Build docker images, pushing, with platform linux/amd64,linux/arm64 and with tag registry-url/application-name:tag-latest

Let we see more details: First we run the tonistiigi/binfmt:latest

Then create our builder

dedyms@homelab docker-gitlab-local % docker buildx create --name MultiArch
MultiArch

Remember our Dockerfile before? we need to remove the ARCH

FROM debian:latest
RUN apt update && apt install -y python3-minimal && apt clean && rm -rf /var/lib/apt/lists/* && mkdir /data
WORKDIR /data
CMD ["python3","-m","http.server"]

Now lets build the image:

oh my gosh i forgot run docker buildx use MultiArch

Lets run it again: progressing....

finished

Now lets inspect the image, here im using the image that already pushed, you may replace the registry-url/application-name:tag-latest to yours

dedyms@homelab apptest % docker buildx imagetools inspect martadinata666/python-http-server:latest                                  
Name:      docker.io/martadinata666/python-http-server:latest
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest:    sha256:447c287bcea699a7403990d9a75b4553e91d4dcc9ba0241bdb50c94e8d26f1e0

Manifests: 
  Name:      docker.io/martadinata666/python-http-server:latest@sha256:d1ab736ab3b53005fce1161474716b152749bff4aa56d9cc490c7187ce59a9f1
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm64

  Name:      docker.io/martadinata666/python-http-server:latest@sha256:3dcef16799d429101ee2a04690d3720e88c7e2919a6621e43a7e4b8f9072fb25
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/amd64

sources:

• multi arch with manifest
• buildx references
• buildx download