chore: switch to multiarch Docker image

Dockerfile

@@ -1,31 +1,88 @@
-FROM rust:1.83-alpine3.21 AS builder
+# This Dockerfile supports building multi-platform Rust applications for
+# linux/amd64 and linux/arm64. It was largely inspired by the article linked
+# below, with the difference being that it more closely follows Docker's
+# caching system. In theory, it can support any architecture that Docker and
+# Rust both support.
+#
+# All RUN directives that require the specific target platform modify the
+# TARGETPLATFORM argument using a sed command. This is required because Rust
+# and Docker use different names for referring to the same architecture. 
+# 
+# https://dev.to/vladkens/fast-multi-arch-docker-build-for-rust-projects-an1
 
-ARG DI_VER=1.2.5
+# We first create a base image that installs Zig (for zig cc) and Cargo Chef
+# (for better dependency caching). This image is shared between all
+# architectures.
+FROM --platform=$BUILDPLATFORM rust:1.88-alpine3.21 AS chef
 
 WORKDIR /app
 
-RUN apk update && apk add --no-cache build-base
+RUN apk update && \
+    apk add --no-cache build-base musl-dev openssl-dev zig && \
+    cargo install --locked cargo-zigbuild cargo-chef
 
-# Build dumb-init
-RUN wget -O - "https://github.com/Yelp/dumb-init/archive/refs/tags/v${DI_VER}.tar.gz" | tar -xzf - && \
+
+# The planner generates the Chef recipe.json file that allows the builder steps
+# to efficiently cache dependency builds, greatly speeding up builds if
+# dependencies haven't changed. This image is also shared between all
+# dependencies.
+FROM chef AS planner
+
+COPY . .
+
+RUN cargo chef prepare --recipe-path recipe.json
+
+
+# The builder container is responsible for performing the actual build. It
+# installs its respective Rust toolchain and builds dumb-init for the target
+# platform. Then it uses the generated Chef recipe file to build the
+# dependencies, before using zigbuild to build the actual final binary.
+FROM chef AS builder
+
+ARG DI_VER=1.2.5
+ARG TARGETPLATFORM
+
+RUN export ARCH="$(echo "${TARGETPLATFORM}" | sed 's:linux/amd64:x86_64:;s:linux/arm64:aarch64:')" && \
+    rustup target add "$ARCH-unknown-linux-musl" && \
+    wget -O - "https://github.com/Yelp/dumb-init/archive/refs/tags/v${DI_VER}.tar.gz" | tar -xzf - && \
     cd "dumb-init-${DI_VER}" && \
-    make SHELL=/bin/sh && \
-    mv dumb-init .. && \
+    make CC="zig cc -target $ARCH-linux-musl" SHELL=/bin/sh && \
+    mkdir -p "/app/${TARGETPLATFORM}" && \
+    mv dumb-init "/app/${TARGETPLATFORM}/dumb-init" && \
     cd ..
 
-COPY Cargo.toml Cargo.lock ./
+# Using Chef, we can build the dependencies separately from the application
+# itself. This allows dependency builds to be cached, greatly speeding up
+# builds when dependencies haven't changed. Zigbuild is used to support
+# building C-based dependencies, such as libsqlite3.
+COPY --from=planner /app/recipe.json recipe.json
 
-RUN cargo fetch --locked
+RUN export ARCH="$(echo "${TARGETPLATFORM}" | sed 's:linux/amd64:x86_64:;s:linux/arm64:aarch64:')" && \
+    cargo chef cook \
+    --recipe-path recipe.json \
+    --release --zigbuild \
+    --target "$ARCH-unknown-linux-musl"
 
-COPY . ./
+# Finally we copy the application source code and build the application binary,
+# using the cached dependency build.
+COPY . .
 
-RUN cargo build --release --frozen
+RUN export ARCH="$(echo "${TARGETPLATFORM}" | sed 's:linux/amd64:x86_64:;s:linux/arm64:aarch64:')" && \
+    cargo zigbuild \
+        --release \
+        --target "$ARCH-unknown-linux-musl" && \
+    cp target/"$ARCH-unknown-linux-musl"/release/site "/app/${TARGETPLATFORM}/site"
 
 
+# We generate the final Alpine-based image by copying the built binaries from
+# the respective target platform's builder container. This is the only part of
+# the build that runs inside an emulator.
 FROM alpine:3.21
 
-COPY --from=builder /app/target/release/site /bin/site
-COPY --from=builder /app/dumb-init /bin/dumb-init
+ARG TARGETPLATFORM
+
+COPY --from=builder /app/${TARGETPLATFORM}/dumb-init /bin/dumb-init
+COPY --from=builder /app/${TARGETPLATFORM}/site /bin/site
 
 # Create a non-root user & make sure it can write to the data directory
 RUN set -x && \
@@ -41,5 +98,3 @@ USER www-data:www-data
 
 ENTRYPOINT [ "/bin/dumb-init", "--" ]
 CMD [ "/bin/site" ]
-
-

Justfile

@@ -0,0 +1,6 @@
+# Build the multi-arch release OCI image and push it to the registry
+push-release-image:
+    docker buildx build \
+        --platform linux/amd64,linux/arm64 \
+        -t chewingbever/site:latest \
+        --push .