docker: Add arm64 builds to Dockerfile and CI

Convert Dockerfile so multiple target architecturebuilds are possible. Also
modify the CI pipeline, in order to built a single multi-platform container.

Note that at the current time-being docker cannot export multi-platform
containers without an intermediate registry. Thus only the amd64 image
is exported for the test stage. Nevertheless the arm64 image is built in
the pipeline and also published later to the registry.

Co-authored-by: Thomas Böhler <t.boehler@kunbus.com>
Signed-off-by: Nicolai Buchwitz <n.buchwitz@kunbus.com>

.github/workflows/ci.yaml

@@ -51,6 +51,9 @@ jobs:
       - name: Repository checkout
         uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
       - name: Setup Docker buildx
         uses: docker/setup-buildx-action@v3
 
@@ -67,6 +70,26 @@ jobs:
           push: false
           pull: true
           file: docker/Dockerfile
+          platforms: linux/amd64,linux/arm64
+          tags: debos
+          cache-from: type=local,src=/tmp/.build-cache
+          cache-to: type=local,dest=/tmp/.build-cache,mode=max
+
+      # WORKAROUND:
+      # Docker buildx cannot export multi-platform images with type=docker,
+      # but only with type=oci. The latter cannot be imported without an
+      # intermediate registry. Thus export only the amd64 image for usage
+      # in the test stage.
+      #
+      # see https://docs.docker.com/reference/cli/docker/buildx/build/#docker
+      - name: Export amd64 Docker image for later usage
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: false
+          pull: true
+          file: docker/Dockerfile
+          platforms: linux/amd64
           tags: debos
           cache-from: type=local,src=/tmp/.build-cache
           cache-to: type=local,dest=/tmp/.build-cache,mode=max
@@ -158,6 +181,7 @@ jobs:
         with:
           name: debos-image
           path: /tmp
+
       - name: Load image
         run: |
           docker load --input /tmp/debos-image.tar
@@ -241,6 +265,7 @@ jobs:
         with:
           context: .
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           file: docker/Dockerfile
@@ -320,6 +345,7 @@ jobs:
         with:
           context: .
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
           file: docker/Dockerfile

docker/Dockerfile

@@ -1,9 +1,10 @@
 # Global ARGs shared by all stages
+ARG ARCH=
 ARG DEBIAN_FRONTEND=noninteractive
 ARG GOPATH=/usr/local/go
 
 ### first stage - builder ###
-FROM debian:bookworm-slim as builder
+FROM ${ARCH}debian:bookworm-slim AS builder
 
 ARG DEBIAN_FRONTEND
 ARG GOPATH
@@ -34,7 +35,24 @@ COPY docker/get-archlinux-keyring.sh /
 RUN /get-archlinux-keyring.sh /arch-keyring
 
 ### second stage - runner ###
-FROM debian:bookworm-slim as runner
+FROM ${ARCH}debian:bookworm-slim AS runner-amd64
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        linux-image-amd64 \
+        qemu-system-x86 \
+        user-mode-linux && \
+    rm -rf /var/lib/apt/lists/*
+
+FROM ${ARCH}debian:bookworm-slim AS runner-arm64
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+        linux-image-arm64 \
+        qemu-system-arm \
+       # fixes: qemu-system-aarch64: failed to find romfile "efi-virtio.rom"
+       ipxe-qemu && \
+    rm -rf /var/lib/apt/lists/*
+
+FROM runner-${TARGETARCH} AS runner
 
 ARG DEBIAN_FRONTEND
 ARG GOPATH
@@ -78,11 +96,9 @@ RUN apt-get update && \
         pigz \
         libostree-1-1 \
         libslirp-helper \
-        linux-image-amd64 \
         openssh-client \
         parted \
         pkg-config \
-        qemu-system-x86 \
         qemu-user-static \
         qemu-utils \
         rsync \
@@ -91,7 +107,6 @@ RUN apt-get update && \
         systemd-resolved \
         u-boot-tools \
         unzip \
-        user-mode-linux \
         xfsprogs \
         xz-utils \
         zip \