Fix #29: revamp Dockerfile to support both x86_64 and aarch64

Dockerfile

@@ -1,31 +1,49 @@
+# Cross-compile Dockerfile supporting both x86_64-unknown-linux-musl and
+# aarch64-unknown-linux-musl using zig to link against musl libc.
+
 # --- build image
 
 FROM rust:1.90 AS builder
 
-RUN rustup target add x86_64-unknown-linux-musl
-RUN apt update && apt install -y musl-tools musl-dev
+RUN rustup target add \
+    aarch64-unknown-linux-musl \
+    x86_64-unknown-linux-musl
+
 RUN update-ca-certificates
 
-ENV USER=app
-ENV UID=10001
+ENV ZIGVERSION=0.15.2
+
+RUN wget https://ziglang.org/download/$ZIGVERSION/zig-x86_64-linux-$ZIGVERSION.tar.xz && \
+    tar -C /usr/local --strip-components=1 -xf zig-x86_64-linux-$ZIGVERSION.tar.xz && \
+    mv /usr/local/zig /usr/local/bin && \
+    rm zig-x86_64-linux-$ZIGVERSION.tar.xz
+
+RUN cargo install --locked cargo-zigbuild
+
+WORKDIR /app
+
+COPY . .
+
+RUN cargo zigbuild \
+    --release \
+    --target aarch64-unknown-linux-musl \
+    --target x86_64-unknown-linux-musl \
+    --bin wastebin \
+    --bin wastebin-ctl
 
 RUN adduser \
     --disabled-password \
     --gecos "" \
     --home "/nonexistent" \
     --shell "/sbin/nologin" \
     --no-create-home \
-    --uid "${UID}" \
-    "${USER}"
+    --uid "10001" \
+    "app"
 
-WORKDIR /app
-COPY . .
-RUN cargo build --target x86_64-unknown-linux-musl --release
 
+# --- x86_64-unknown-linux-musl final image
 
-# --- final image
-
-FROM scratch
+FROM scratch AS amd64
 
 COPY --from=builder /etc/passwd /etc/passwd
 COPY --from=builder /etc/group /etc/group
@@ -35,3 +53,16 @@ COPY --from=builder /app/target/x86_64-unknown-linux-musl/release/wastebin ./
 COPY --from=builder /app/target/x86_64-unknown-linux-musl/release/wastebin-ctl ./
 USER app:app
 CMD ["/app/wastebin"]
+
+# --- aarch64-unknown-linux-musl final image
+
+FROM scratch AS arm64
+
+COPY --from=builder /etc/passwd /etc/passwd
+COPY --from=builder /etc/group /etc/group
+
+WORKDIR /app
+COPY --from=builder /app/target/aarch64-unknown-linux-musl/release/wastebin ./
+COPY --from=builder /app/target/aarch64-unknown-linux-musl/release/wastebin-ctl ./
+USER app:app
+CMD ["/app/wastebin"]