1.Dockerfile

#syntax=docker/dockerfile:1.7.0

# Example of Dockerfile that uses a custom command for Risc-V
# and different shared command for other architectures

ARG ARCH=${TARGETARCH#riscv64}
ARG ARCH=${ARCH:+"common"}
ARG ARCH=${ARCH:-$TARGETARCH}

FROM --platform=$BUILDPLATFORM alpine AS base-common
ARG TARGETARCH
RUN echo "Common build, I am $TARGETARCH" > /out

FROM --platform=$BUILDPLATFORM alpine AS base-riscv64
ARG TARGETARCH
RUN echo "Riscv only special build, I am $TARGETARCH" > /out

FROM base-${ARCH} AS base

FROM scratch
COPY --from=base /out /out

1.out

» docker buildx build --platform linux/amd64,linux/arm64,linux/arm,linux/s390x,linux/riscv64 -o out -f 1.Dockerfile .

» find . -type f -name out -exec sh -c 'echo "{}"; cat "{}"' \;
./out/linux_arm_v7/out
Common build, I am arm
./out/linux_arm64/out
Common build, I am arm64
./out/linux_riscv64/out
Riscv only special build, I am riscv64
./out/linux_s390x/out
Common build, I am s390x
./out/linux_amd64/out
Common build, I am amd64

2.Dockerfile

#syntax=docker/dockerfile:1.7.0

# Example of Dockerfile that uses a custom command for Risc-V and S390x
# and different shared command for the rest of the architectures

ARG ARCH=${TARGETARCH#riscv64}
ARG ARCH=${ARCH#s390x}
ARG ARCH=${ARCH:+"common"}
ARG ARCH=${ARCH:-$TARGETARCH}

FROM --platform=$BUILDPLATFORM alpine AS base-common
ARG TARGETARCH
RUN echo "Common build, I am $TARGETARCH" > /out

FROM --platform=$BUILDPLATFORM alpine AS base-riscv64
ARG TARGETARCH
RUN echo "Riscv only special build, I am $TARGETARCH" > /out

FROM --platform=$BUILDPLATFORM alpine AS base-s390x
ARG TARGETARCH
RUN echo "IBM only special build, I am $TARGETARCH" > /out

FROM base-${ARCH} AS base

FROM scratch
COPY --from=base /out /out

2.out

» docker buildx build --platform linux/amd64,linux/arm64,linux/arm,linux/s390x,linux/riscv64 -o out -f 2.Dockerfile .

» find . -type f -name out -exec sh -c 'echo "{}"; cat "{}"' \;
./out/linux_arm_v7/out
Common build, I am arm
./out/linux_arm64/out
Common build, I am arm64
./out/linux_riscv64/out
Riscv only special build, I am riscv64
./out/linux_s390x/out
IBM only special build, I am s390x
./out/linux_amd64/out
Common build, I am amd64

3.Dockerfile

#syntax=docker/dockerfile:1.7.0

# Example of Dockerfile that uses a custom command for Risc-V
# and for 32bit ARM but only if it is v5 variant and different
# shared command for the rest of the architectures

ARG ARCH=${TARGETARCH}${TARGETVARIANT}
ARG ARCH=${ARCH#riscv64}
ARG ARCH=${ARCH#armv5}
ARG ARCH=${ARCH:+common}
ARG ARCH=${ARCH:-$TARGETARCH$TARGETVARIANT}

FROM --platform=$BUILDPLATFORM alpine AS base-common
ARG TARGETPLATFORM
RUN echo "Common build, I am $TARGETPLATFORM" > /out

FROM --platform=$BUILDPLATFORM alpine AS base-riscv64
ARG TARGETPLATFORM
RUN echo "Riscv only special build, I am $TARGETPLATFORM" > /out

FROM --platform=$BUILDPLATFORM alpine AS base-armv5
ARG TARGETPLATFORM
RUN echo "Old arm only special build, I am $TARGETPLATFORM" > /out

FROM base-${ARCH} AS base

FROM scratch
COPY --from=base /out /out

3.out

» docker buildx build --platform linux/amd64,linux/arm64,linux/arm,linux/s390x,linux/riscv64,linux/arm/v5,linux/arm/v6 -o out -f 3.Dockerfile .

» find . -type f -name out -exec sh -c 'echo "{}"; cat "{}"' \;
./out/linux_arm_v7/out
Common build, I am linux/arm/v7
./out/linux_arm_v6/out
Common build, I am linux/arm/v6
./out/linux_arm64/out
Common build, I am linux/arm64
./out/linux_riscv64/out
Riscv only special build, I am linux/riscv64
./out/linux_s390x/out
Common build, I am linux/s390x
./out/linux_amd64/out
Common build, I am linux/amd64
./out/linux_arm_v5/out
Old arm only special build, I am linux/arm/v5