Simplify docker build

Previously, one command for each platform was needed to build the
images, followed by the need to create manifest manually.

It is possible to simplify this, while making the build faster, by
moving the arch specific build-arg into the Dockerfile directly, and
using the build platform's architecture for the downloader to share the
cache between the target architure images.

Dockerfile

@@ -5,7 +5,22 @@
 # * final: Copy the binaries required at runtime
 # The resulting image uploaded to dockerhub will only contain what is needed for runtime.
 # From the root of the repository, run "docker build -t yourimage:yourtag ."
-FROM debian:bullseye-slim as downloader
+
+FROM --platform=$BUILDPLATFORM debian:bullseye-slim as base-downloader
+RUN set -ex \
+	&& apt-get update \
+	&& apt-get install -qq --no-install-recommends ca-certificates dirmngr wget
+
+FROM --platform=$BUILDPLATFORM base-downloader as base-downloader-linux-amd64
+ENV TARBALL_ARCH_FINAL=x86_64-linux-gnu
+
+FROM --platform=$BUILDPLATFORM base-downloader as base-downloader-linux-arm64
+ENV TARBALL_ARCH_FINAL=aarch64-linux-gnu
+
+FROM --platform=$BUILDPLATFORM base-downloader as base-downloader-linux-arm
+ENV TARBALL_ARCH_FINAL=arm-linux-gnueabihf
+
+FROM base-downloader-${TARGETOS}-${TARGETARCH} as downloader
 
 RUN set -ex \
 	&& apt-get update \
@@ -15,8 +30,6 @@ WORKDIR /opt
 
 
 ARG BITCOIN_VERSION=22.0
-ARG TARBALL_ARCH=x86_64-linux-gnu
-ENV TARBALL_ARCH_FINAL=$TARBALL_ARCH
 ENV BITCOIN_TARBALL bitcoin-${BITCOIN_VERSION}-${TARBALL_ARCH_FINAL}.tar.gz
 ENV BITCOIN_URL https://bitcoincore.org/bin/bitcoin-core-$BITCOIN_VERSION/$BITCOIN_TARBALL
 ENV BITCOIN_ASC_URL https://bitcoincore.org/bin/bitcoin-core-$BITCOIN_VERSION/SHA256SUMS

tools/build-release.sh

@@ -175,61 +175,17 @@ done
 if [ -z "${TARGETS##* docker *}" ]; then
     echo "Building Docker Images"
     DOCKER_USER="elementsproject"
-    PLATFORMS="amd64 arm64v8"
-    for d in $PLATFORMS; do
-        TMPDIR="$(mktemp -d /tmp/lightningd-docker-"$d".XXXXXX)"
-        SRCDIR="$(pwd)"
-        echo "Bundling $d image in ${TMPDIR}"
-        git clone --recursive . "${TMPDIR}"
-        (
-        cd "${TMPDIR}"
-        if ! $FORCE_UNCLEAN; then
-            git checkout "v${BARE_VERSION}"
-        fi
-        cp "${SRCDIR}/Dockerfile" "${TMPDIR}/"
-        case "$d" in
-            "arm32v7")
-                TARBALL_ARCH="arm-linux-gnueabihf"
-                PLATFORM="linux/arm/v7"
-                ;;
-            "arm64v8")
-                TARBALL_ARCH="aarch64-linux-gnu"
-                PLATFORM="linux/arm64"
-                ;;
-            "amd64")
-                TARBALL_ARCH="x86_64-linux-gnu"
-                PLATFORM="linux/amd64"
-                ;;
-        esac
-        if $DOCKER_PUSH; then
-            docker buildx build --push --platform $PLATFORM --build-arg TARBALL_ARCH=$TARBALL_ARCH -t "$DOCKER_USER"/lightningd:"$VERSION"-"$d" -f Dockerfile "${TMPDIR}"
-            echo "Docker Image for $PLATFORM Built and Uploaded on Dockerhub."
-        else
-            docker buildx build --load --platform $PLATFORM --build-arg TARBALL_ARCH=$TARBALL_ARCH -t "$DOCKER_USER"/lightningd:"$VERSION"-"$d" -f Dockerfile "${TMPDIR}"
-            echo "Docker Image for $PLATFORM Built. Ready to Upload on Dockerhub."
-        fi
-        )
-        rm -rf "${TMPDIR}"
-    done
     echo "Creating a multi-platform image tagged as $VERSION"
-    docker manifest create --amend "$DOCKER_USER"/lightningd:"$VERSION" "$DOCKER_USER"/lightningd:"$VERSION"-amd64 "$DOCKER_USER"/lightningd:"$VERSION"-arm64v8
-    docker manifest annotate "$DOCKER_USER"/lightningd:"$VERSION" "$DOCKER_USER"/lightningd:"$VERSION"-amd64 --os linux --arch amd64
-    docker manifest annotate "$DOCKER_USER"/lightningd:"$VERSION" "$DOCKER_USER"/lightningd:"$VERSION"-arm64v8 --os linux --arch arm64 --variant v8
-    # FIXME: Throws ERROR: failed to solve: debian:bullseye-slim: no match for platform in manifest
-    # docker buildx create --use
-    # docker buildx build --push --platform linux/amd64,linux/arm64v8 -t "$DOCKER_USER/lightningd:"$VERSION"-$d" .
-    echo "Creating a multi-platform image tagged as latest"
-    # Remove the old image
-    docker rmi "$DOCKER_USER"/lightningd:latest
-    # Remove the old manifest
-    docker manifest rm "$DOCKER_USER"/lightningd:latest
-    docker manifest create "$DOCKER_USER"/lightningd:latest "$DOCKER_USER"/lightningd:"$VERSION"-amd64 "$DOCKER_USER"/lightningd:"$VERSION"-arm64v8
-    docker manifest annotate "$DOCKER_USER"/lightningd:latest "$DOCKER_USER"/lightningd:"$VERSION"-amd64 --os linux --arch amd64
-    docker manifest annotate "$DOCKER_USER"/lightningd:latest "$DOCKER_USER"/lightningd:"$VERSION"-arm64v8 --os linux --arch arm64 --variant v8
+    DOCKER_OPTS="--platform linux/amd64,linux/arm64"
+    $DOCKER_PUSH && DOCKER_OPTS="$DOCKER_OPTS --push"
+    DOCKER_OPTS="$DOCKER_OPTS -t $DOCKER_USER/lightningd:$VERSION"
+    DOCKER_OPTS="$DOCKER_OPTS -t $DOCKER_USER/lightningd:latest"
+
+    docker buildx create --use
+    # shellcheck disable=SC2086
+    docker buildx build $DOCKER_OPTS .
+
     if $DOCKER_PUSH; then
-        docker manifest push "$DOCKER_USER"/lightningd:"$VERSION"
-        echo "Pushed a multi-platform image tagged as $VERSION"
-        docker manifest push "$DOCKER_USER"/lightningd:latest
         echo "Pushed a multi-platform image tagged as latest"
     else
         echo "Docker Images Built. Ready to Upload on Dockerhub."