Crossplatform docker build

A docker image can be build for a desired platform by adding the --platform parameter:

docker build . --file Dockerfile --tag <my_tag> --platform=arm64

Note: If you are getting "/bin/sh: exec format error" error during build, you are probably lacking a package that can be installed by:

sudo apt install qemu-user-static

The crossplatform build is facilitated by QEMU. Expect a run-time approx. 10x slower than for your native platform.

Multi-platform docker build

Multi-platform images can be built using the dockerx multiplatform builder. First, instantiate a multiplatform builder and set it to be the default (--use):

docker buildx create --name container-builder --driver docker-container --bootstrap --use
docker buildx use container-builder

Then, build an image using the buildx command (which uses the selected builder) and supply the --platform parameter with the list of the desired platforms. We usually --push the image immediately after the build into a docker registry.

docker buildx build . --file Dockerfile --tag <my_tag> --platform=linux/arm64,linux/amd64 --push

Do not forget to change the default builder back into the original builder (probably default) after you finish with the multiplatform build.

Listing the available docker builders

docker buildx ls

NAME/NODE                DRIVER/ENDPOINT                   STATUS    BUILDKIT   PLATFORMS
container-builder        docker-container
 \_ container-builder0    \_ unix:///var/run/docker.sock   running   v0.16.0    linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/amd64/v4, linux/arm64, linux/riscv64, linux/ppc64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
 default*                 docker
  \_ default               \_ default                       running   v0.16.0    linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/amd64/v4, linux/arm64, linux/riscv64, linux/ppc64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6

If you want to switch back to the default docker builder, select it then by issuing

docker buildx use default