Support automated multi-arch builds on Docker Hub

Author: ckulka

Multi-Arch-Builds-on-Docker-Hub.md

@@ -0,0 +1,43 @@
+# Multi-arch builds on Docker Hub
+
+The [Custom build phase hooks](https://docs.docker.com/docker-hub/builds/advanced/#override-build-test-or-push-commands) build all variants for all platforms, e.g. `amd64` and `arm32v7`, on Docker Hub.
+
+More specifically, the hooks
+
+- Build the image variants in the `build` phase
+- Push all images in the `push` phase
+- Update the multi-arch manifest in the `post_push` phase
+
+The `post_push` hook generates and pushes the manifest which - simply put - is just a list of references to other images.
+
+```yaml
+# Manifest for resilio/sync:release-2.6.3 which points to the amd64 and arm32v7 images
+image: resilio/sync:release-2.6.3
+manifests:
+  - image: resilio/sync:release-2.6.3-amd64
+    platform:
+      architecture: amd64
+      os: linux
+  - image: resilio/sync:release-2.6.3-arm32v7
+    platform:
+      architecture: arm
+      os: linux
+      variant: v7
+```
+
+## Setting up Docker Hub Automated Builds
+
+The following Docker Hub configuration for Automated Builds results in the tags listed in the [README.md](./README.md).
+
+| Source Type | Source | Docker Tag          | Dockerfile location | Build Context |
+| ----------- | ------ | ------------------- | ------------------- | ------------- |
+| Branch      | master | latest              | Dockerfile          | /             |
+| Tag         | /.\*/  | release-{sourceref} | Dockerfile          | /             |
+
+The `master` branch creates the multi-arch `latest` image and its the platform specific `latest-*` variants.
+
+The tags are published as `release-*` images, e.g. the Git tag `2.6.3` creates the multi-arch `release-2.6.3` image and its platform specific `release-2.6.3-*` variants.
+
+## References
+
+For more details, see [Advanced options for Autobuild and Autotest](https://docs.docker.com/docker-hub/builds/advanced/).

hooks/build

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# Custom build script to build images for all supported architectures.
+#
+# Example for IMAGE_NAME: resilio/sync:release-2.6.3
+# Images built:
+# - resilio/sync:release-2.6.3-amd64
+# - resilio/sync:release-2.6.3-arm32v7
+
+for arch in amd64 arm32v7
+do
+  echo "Building $IMAGE_NAME-$arch"
+  docker build --build-arg FROM_ARCH=$arch --file $DOCKERFILE_PATH --tag $IMAGE_NAME-$arch .
+done

hooks/post_push

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+echo "Pushing multi-arch manifest $IMAGE_NAME"
+
+# Use manifest-tool to create the manifest, given the experimental
+# "docker manifest" command isn't available yet on Docker Hub.
+curl -Lo manifest-tool https://github.com/estesp/manifest-tool/releases/download/v0.9.0/manifest-tool-linux-amd64
+chmod +x manifest-tool
+
+cat > manifest-generated.yaml << EOF
+image: $IMAGE_NAME
+manifests:
+  - image: $IMAGE_NAME-amd64
+    platform:
+      architecture: amd64
+      os: linux
+  - image: $IMAGE_NAME-arm32v7
+    platform:
+      architecture: arm
+      os: linux
+      variant: v7
+EOF
+
+./manifest-tool push from-spec manifest-generated.yaml

hooks/pre_build

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+# Register qemu-*-static for all supported processors except the
+# current one, but also remove all registered binfmt_misc before
+docker run --rm --privileged multiarch/qemu-user-static:register --reset

hooks/push

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# Custom build script to push images for all supported architectures.
+#
+# Example for IMAGE_NAME: resilio/sync:release-2.6.3
+# Images pushed:
+# - resilio/sync:release-2.6.3-amd64
+# - resilio/sync:release-2.6.3-arm32v7
+
+for arch in amd64 arm32v7
+do
+  echo "Pushing $IMAGE_NAME-$arch"
+  docker push $IMAGE_NAME-$arch
+done