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Multi-platform Docker image build on aarch64

Multi-stage and multi-platform Dockerfile is awesome
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I use Jenkins CI/CD platform for my hobby projects on aarch64 (linux/arm64v8) architecture. But I run these images on linux/amd64 at the most of time. So, I need to use multi-stage Dockerfile to build image for multi-platform. After some Google search and check results, I found a great blog post about this topic on the Docker website. The title of the article is Faster Multi-Platform Builds: Dockerfile Cross-Compilation Guide.

First of all, you can check on your OS and Docker environment, how to setup correctly the docker buildx, please see this builder toolkit page.

docker buildx ls

You can access the following build ARGs in your Dockerfile:

BUILDPLATFORM — matches the current machine. (e.g. linux/amd64)
BUILDOS — os component of BUILDPLATFORM, e.g. linux
BUILDARCH — e.g. amd64, arm64, riscv64
BUILDVARIANT — used to set ARM variant, e.g. v7
TARGETPLATFORM — The value set with --platform flag on build
TARGETOS - OS component from --platform, e.g. linux
TARGETARCH - Architecture from --platform, e.g. arm64
TARGETVARIANT

Here is the minimal setup for Dockerfile to test on your system.

FROM --platform=$BUILDPLATFORM golang:alpine AS build
ARG TARGETPLATFORM
ARG BUILDPLATFORM
RUN echo "I am running on $BUILDPLATFORM, building for $TARGETPLATFORM" > /log
FROM alpine
COPY --from=build /log /log

After you log in docker or private registry, run this command: docker buildx build --platform linux/amd64,linux/arm64 --push .

Unfortunately, we can store multi-platform images only in registry.

Build multi-stage Dockerfile for golang app

FROM --platform=$BUILDPLATFORM golang:1.17-alpine AS builder
WORKDIR /src
ARG TARGETOS TARGETARCH
RUN --mount=target=. 
    --mount=type=cache,target=/root/.cache/go-build 
    --mount=type=cache,target=/go/pkg 
    GOOS=$TARGETOS GOARCH=$TARGETARCH go build -o /out/myapp .

FROM alpine as runner
COPY --from=builder /out/myapp /bin

EXPOSE 8080

CMD ["myapp"]

Final words

If the programming languages and the native libraries don’t support cross-compilation, then there are still plenty of problems with it and the working solution isn’t simple.

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