cross-build-dockerfile-with-args

cross-build-dockerfile-with-args

$ cat <<EOF >> Dockerfile
FROM alpine
ARG TARGETPLATFORM
ARG TARGETOS
ARG TARGETARCH
ARG TARGETVARIANT

ARG BUILDPLATFORM
ARG BUILDOS
ARG BUILDARCH
ARG BUILDVARIANT

RUN echo "Image target platform details :: "
RUN echo "TARGETPLATFORM    : $TARGETPLATFORM"
RUN echo "TARGETOS          : $TARGETOS"
RUN echo "TARGETARCH        : $TARGETARCH"
RUN echo "TARGETVARIANT     : $TARGETVARIANT"

RUN echo "Image build platform details :: "
RUN echo "BUILDPLATFORM     : $BUILDPLATFORM"
RUN echo "BUILDOS           : $BUILDOS"
RUN echo "BUILDARCH         : $BUILDARCH"
RUN echo "BUILDVARIANT      : $BUILDVARIANT"
EOF

$ docker buildx create --name my-new-builder --driver docker-container --use
$ docker buildx inspect --bootstrap
$ docker buildx build --platform=linux/amd64,linux/arm64,linux/s390x --push -t <dockerhub_id>/my-image:latest .

When building an image with multiple platform targets, you might in some cases require to know what the building platform is and what the target platform is, there are a few arguments that are injected when running buildx build, and those are the following:

TARGETPLATFORM # Platform of the target, for example: 'linux/arm64' or `linux/arm/v7` 
TARGETOS       # Os part of the target platform, for example: 'linux' or 'windows'
TARGETARCH     # Arch part of the target platform, for example 'amd64', 'arm64' or 'arm'
TARGETVARIANT  # If the target platform have a variant (`v7` in arm for example), this will be set to that value
BUILDPLATFORM  # The platform of the build machine
BUILDOS        # OS of the build machine
BUILDARCH      # Architecture of the build machine
BUILDVARIANT   # Variant (if exist) of the build machine

As usual, you should define those with the ARG directive in your image, else they will not be available to use.

Link: https://jite.eu/2019/10/3/multi-arch-docker/