Improved generator docker build by caching dependencies

Apps/generator/Dockerfile

@@ -1,16 +1,39 @@
-# Use official rust:slim as base
-FROM rust:slim
+################
+##### Builder
+FROM rust:slim as builder
 
+WORKDIR /usr/src
 
-# Create folder structur for code
-RUN mkdir -p /usr/src/generator
+# Create blank project
+RUN USER=root cargo new generator
+
+# We want dependencies cached, so copy those first.
+COPY Cargo.toml Cargo.lock /usr/src/generator/
+
+# Set the working directory
 WORKDIR /usr/src/generator
 
-# Copy source code onto docker image
-COPY . .
+## Install target platform (Cross-Compilation) --> Needed for Alpine
+RUN rustup target add x86_64-unknown-linux-musl
+
+# This is a dummy build to get the dependencies cached.
+RUN cargo build --target x86_64-unknown-linux-musl --release
+
+# Now copy in the rest of the sources
+COPY src /usr/src/generator/src/
+
+## Touch main.rs to prevent cached release build
+RUN touch /usr/src/generator/src/main.rs
+
+# This is the actual application build.
+RUN cargo build --target x86_64-unknown-linux-musl --release
+
+################
+##### Runtime
+FROM alpine:3.16.0 AS runtime 
 
-# Build
-RUN cargo build
+# Copy application binary from builder image
+COPY --from=builder /usr/src/generator/target/x86_64-unknown-linux-musl/release/generator /usr/local/bin
 
-# Run on container start
-CMD ["cargo", "run"]
+# Run the application
+CMD ["/usr/local/bin/generator"]