Docker, Cargo: Add multi-arch builds for arm64, x86_64

Builds static binaries instead to be runnable from scratch. This eases
the build process, as we don't have to depend on docker's buildx.
Now images for both arm64 and x86_64 can be built on x86_64 platform
alone.

Signed-off-by: Gunwant Jain <mail@wantguns.dev>

.cargo/config.toml

@@ -0,0 +1,7 @@
+[build]
+target = "x86_64-unknown-linux-gnu"
+rustflags = ["-C", "target-feature=+crt-static"]
+
+[target.aarch64-unknown-linux-gnu]
+linker = "aarch64-linux-gnu-gcc"
+rustflags = ["-C", "target-feature=+crt-static"]

Dockerfile

@@ -1,12 +1,30 @@
-FROM rust:1 as builder
+###### Builder Image
+FROM rust as builder
 WORKDIR /app
 COPY . .
-RUN RUSTFLAGS='-C target-feature=+crt-static' cargo install --target x86_64-unknown-linux-gnu --path .
+# scratch does not have the mkdir binary, so we create a folder here
+RUN mkdir -p empty_upload
+
+ARG ARCH
+RUN __ARCH="$(dpkg --print-architecture)"; \
+    [ -z  $ARCH ] || __ARCH=$ARCH; \
+    case "$__ARCH" in \
+        arm64) \
+            export __TARGET='aarch64-unknown-linux-gnu'; \
+            apt update && apt upgrade -y; \
+            apt install -y gcc-aarch64-linux-gnu; \
+            rustup target add aarch64-unknown-linux-gnu; \
+            ;; \
+        amd64) export __TARGET='x86_64-unknown-linux-gnu' ;; \
+    esac; \
+    cargo install --target $__TARGET --path .;
+
 RUN cargo clean
 
-FROM debian:buster-slim as runner
-WORKDIR /app
-RUN mkdir -p upload
+
+###### Runner Image
+FROM scratch as runner
+COPY --from=builder /app/empty_upload upload
 COPY ./client upload/client
 COPY ./templates templates
 COPY ./static static