cache rust build dependencies in dockerfile

Dockerfile.rust

@@ -0,0 +1,34 @@
+FROM alpine:latest AS builder
+
+WORKDIR /build
+
+RUN apk add rustup build-base
+# todo: arm64 target
+RUN rustup-init --default-host x86_64-unknown-linux-musl --default-toolchain stable --profile default -y
+
+ENV PATH=/root/.cargo/bin:$PATH
+ENV RUSTFLAGS='-C link-arg=-s'
+
+RUN cargo install cargo-chef --locked
+
+# build dependencies first to cache
+FROM builder AS recipe-builder
+COPY . .
+RUN cargo chef prepare --recipe-path recipe.json
+
+FROM builder AS binary-builder
+COPY --from=recipe-builder /build/recipe.json recipe.json
+RUN cargo chef cook --release --recipe-path recipe.json --target x86_64-unknown-linux-musl
+
+COPY Cargo.toml /build/
+COPY Cargo.lock /build/
+
+# this needs to match workspaces in Cargo.toml
+COPY lib/libpk /build/lib/libpk
+COPY services/api/ /build/services/api
+
+RUN cargo build --bin api --release --target x86_64-unknown-linux-musl
+
+FROM scratch 
+
+COPY --from=binary-builder /build/target/x86_64-unknown-linux-musl/release/api /api