$ 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"
  ]
}

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

Credits to Jérémie Drouet

$ docker build --pull -t registry/docker-with-buildx .
$ docker push registry/docker-with-buildx

Define CI_PLATFORMS variable in Settings / CI/CD:

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

.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 .