Make the Docker image cross-compile without QEMU emulation

.github/workflows/docker.yaml

@@ -16,19 +16,9 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-      - name: Set up QEMU
-        id: qemu
-        uses: docker/setup-qemu-action@v2
-        with:
-          platforms: arm64
-
       - name: Set up Docker Buildx
-        id: buildx
         uses: docker/setup-buildx-action@v2
 
-      - name: Inspect builder
-        run: docker buildx inspect
-
 # Disabled while I wait for IT/SRE to grant perms for this token
 #       - name: Log in to DockerHub
 #         uses: docker/login-action@v2
@@ -65,9 +55,5 @@ jobs:
           labels: "gitsha1=${{ github.sha }}"
           tags: "${{ steps.set-tag.outputs.tags }}"
           platforms: linux/amd64,linux/arm64
-
-          # arm64 builds OOM without the git fetch setting. c.f.
-          # https://github.com/rust-lang/cargo/issues/10583
-          build-args: |
-            CARGO_NET_GIT_FETCH_WITH_CLI=true
-            BUILD_PROFILE=release
+          cache-from: type=registry,ref=ghcr.io/${{ github.repository }}:buildcache
+          cache-to: type=registry,ref=ghcr.io/${{ github.repository }}:buildcache,mode=max

Dockerfile

@@ -1,27 +1,54 @@
-FROM docker.io/rust:alpine AS builder
+# This uses the multi-stage build feature of Docker to build the binaries for multiple architectures without QEMU.
+# The first stage is responsible for building binaries for all the supported architectures (amd64 and arm64), and the
+# second stage only copies the binaries for the target architecture.
+# We leverage Zig and cargo-zigbuild for providing a cross-compilation-capable C compiler and linker.
 
-RUN apk add python3 musl-dev pkgconfig openssl-dev make git
+ARG RUSTC_VERSION=1.72.0
+ARG ZIG_VERSION=0.11.0
+ARG CARGO_ZIGBUILD_VERSION=0.17.1
 
-WORKDIR /opt/synapse-compressor/
-COPY . .
-
-ENV RUSTFLAGS="-C target-feature=-crt-static"
-
-# arm64 builds consume a lot of memory if `CARGO_NET_GIT_FETCH_WITH_CLI` is not
-# set to true, so we expose it as a build-arg.
-ARG CARGO_NET_GIT_FETCH_WITH_CLI=false
-ENV CARGO_NET_GIT_FETCH_WITH_CLI=$CARGO_NET_GIT_FETCH_WITH_CLI
-ARG BUILD_PROFILE=dev
+FROM --platform=${BUILDPLATFORM} docker.io/rust:${RUSTC_VERSION} AS builder
 
-RUN cargo build --profile=$BUILD_PROFILE
+# Install cargo-zigbuild for cross-compilation
+ARG CARGO_ZIGBUILD_VERSION
+RUN cargo install --locked cargo-zigbuild@=${CARGO_ZIGBUILD_VERSION}
 
-WORKDIR /opt/synapse-compressor/synapse_auto_compressor/
+# Download zig compiler for cross-compilation
+ARG ZIG_VERSION
+RUN curl -L "https://ziglang.org/download/${ZIG_VERSION}/zig-linux-$(uname -m)-${ZIG_VERSION}.tar.xz" | tar -J -x -C /usr/local && \
+  ln -s "/usr/local/zig-linux-$(uname -m)-${ZIG_VERSION}/zig" /usr/local/bin/zig
 
-RUN cargo build
+# Install all cross-compilation targets
+ARG RUSTC_VERSION
+RUN rustup target add  \
+    --toolchain "${RUSTC_VERSION}" \
+    x86_64-unknown-linux-musl \
+    aarch64-unknown-linux-musl
 
-FROM docker.io/alpine
-
-RUN apk add --no-cache libgcc
+WORKDIR /opt/synapse-compressor/
+COPY . .
 
-COPY --from=builder /opt/synapse-compressor/target/*/synapse_compress_state /usr/local/bin/synapse_compress_state
-COPY --from=builder /opt/synapse-compressor/target/*/synapse_auto_compressor /usr/local/bin/synapse_auto_compressor
+# Build for all targets
+RUN cargo zigbuild \
+    --release \
+    --workspace \
+    --bins \
+    --features "openssl/vendored" \
+    --target aarch64-unknown-linux-musl \
+    --target x86_64-unknown-linux-musl
+
+# Move the binaries in a separate folder per architecture, so we can copy them using the TARGETARCH build arg
+RUN mkdir -p /opt/binaries/amd64 /opt/binaries/arm64
+RUN mv target/x86_64-unknown-linux-musl/release/synapse_compress_state \
+       target/x86_64-unknown-linux-musl/release/synapse_auto_compressor \
+       /opt/binaries/amd64
+RUN mv target/aarch64-unknown-linux-musl/release/synapse_compress_state \
+       target/aarch64-unknown-linux-musl/release/synapse_auto_compressor \
+       /opt/binaries/arm64
+
+FROM --platform=${TARGETPLATFORM} docker.io/alpine
+
+ARG TARGETARCH
+
+COPY --from=builder /opt/binaries/${TARGETARCH}/synapse_compress_state /usr/local/bin/synapse_compress_state
+COPY --from=builder /opt/binaries/${TARGETARCH}/synapse_auto_compressor /usr/local/bin/synapse_auto_compressor