Very large docker image size optimisations

without cross compiling to linux-musl, optimise image by compiling it on a slim rust image and then transferring only the binary over to a debian-slim image.

Dockerfile

@@ -1,11 +1,21 @@
-FROM rust:1.56
+FROM rust:1.56-slim AS builder
 
 WORKDIR /app
-
 COPY . .
+
 ENV SQLX_OFFLINE true
 RUN cargo build --release
 
+FROM debian:bullseye-slim AS runtime
+
+WORKDIR /app
+
+# Install dependancies required
+RUN apt update -y && apt install -y --no-install-recommends openssl && apt autoremove -y && apt clean -y && rm -rf /var/lib/apt/lists/*
+
+# Copy the fully built binary and configuration to the image
+COPY --from=builder /app/target/release/mail_app mail_app
+COPY configuration configuration 
 ENV APP_ENVIRONMENT production
 
-ENTRYPOINT ["./target/release/mail_app"]
+ENTRYPOINT ["./mail_app"]