====== Gitlab CI MultiPlatform Build ======

===== Enable binary formats =====
<code bash>
$ docker run --rm --privileged tonistiigi/binfmt --install all
{
  "supported": [
    "linux/amd64",
    "linux/arm64",
    "linux/riscv64",
    "linux/ppc64le",
    "linux/s390x",
    "linux/386",
    "linux/arm/v7",
    "linux/arm/v6"
  ],
  "emulators": [
    "qemu-aarch64",
    "qemu-arm",
    "qemu-ppc64le",
    "qemu-riscv64",
    "qemu-s390x"
  ]
}
</code>
===== Create buildx enabled docker image for builds =====
<file bash Dockerfile>
ARG BUILDX_VERSION=0.4.2
ARG DOCKER_VERSION=latest

FROM alpine AS fetcher

RUN apk add curl

ARG BUILDX_VERSION
RUN curl -L \
  --output /docker-buildx \
  "https://github.com/docker/buildx/releases/download/v${BUILDX_VERSION}/buildx-v${BUILDX_VERSION}.linux-amd64"

RUN chmod a+x /docker-buildx

ARG DOCKER_VERSION
FROM docker:${DOCKER_VERSION}

COPY --from=fetcher /docker-buildx /usr/lib/docker/cli-plugins/docker-buildx
</file>

Credits to [[https://github.com/jdrouet|Jérémie Drouet]]

==== Build & push image ====

<code bash>
$ docker build --pull -t registry/docker-with-buildx .
$ docker push registry/docker-with-buildx
</code>

===== Switch to buildx in .gitlab-ci.yml =====
Define CI_PLATFORMS variable in Settings / CI/CD:

CI_PLATFORMS = linux/amd64,linux/arm/v7,...

<file bash .gitlab-ci.yml>
image: registry/docker-with-buildx

services:
  - docker:dind

build:
  stage: build
  script:
    - docker login -u $CI_USER -p $CI_TOKEN $CI_REGISTRY
    - docker buildx create --use
    - docker buildx build --platform $CI_PLATFORMS --push --pull -t $CI_REGISTRY_IMAGE .
</file>
{{tag>kb git}}