Use multi-stage builds

Author: kpcyrd

Dockerfile

@@ -1,10 +1,18 @@
-FROM alpine:latest
-COPY ./ /app
+# Start with a rust alpine image
+FROM rust:1-alpine3.10
+# if needed, install dependencies here
+#RUN apk add libseccomp-dev
+# set the workdir and copy the source into it
 WORKDIR /app
-RUN apk add --no-cache libgcc \
-    && apk add --no-cache --virtual .build-rust rust cargo \
-    && cargo build --release \
-    && cp target/release/mini-docker-rust . \
-    && rm -rf target/ ~/.cargo/ \
-    && apk del --purge .build-rust
-ENTRYPOINT ["./mini-docker-rust"]
+COPY ./ /app
+# do a release build
+RUN cargo build --release
+
+# use a plain alpine image, the alpine version needs to match the builder
+FROM alpine:3.10
+# if needed, install dependencies here
+#RUN apk add libseccomp
+# copy the binary into the final image
+COPY --from=0 /app/target/release/mini-docker-rust .
+# set the binary as entrypoint
+ENTRYPOINT ["/mini-docker-rust"]

README.md

@@ -5,35 +5,12 @@
 
 Very small rust docker image.
 
-This is an example project on how to build very small docker images for a rust project. The resulting image for a working hello world was about 5.87MB during my tests.
+This is an example project on how to build very small docker images for a rust project. The resulting image for a working hello world was about 8.1MB during my tests.
 
 ## See for yourself
 
 You don't need to install anything besides docker. Build with `docker build -t mini-docker-rust .` and run with `docker run mini-docker-rust`.
 
 ## Annotated docker file
 
-```
-# Start with alpine as base image
-FROM alpine:latest
-# Copy our project into the image (see .dockerignore for exclusions)
-COPY ./ /app
-# Switch the current directory to /app
-WORKDIR /app
-# This does multiple things in one go to keep the image size and layer number extremly low:
-# llvm-libunwind is required to run the final rust binary, so we install it first
-RUN apk add --no-cache llvm-libunwind \
-    # Next, we install rust and cargo and tag them in a virtual package called `.build-rust`
-    && apk add --no-cache --virtual .build-rust rust cargo \
-    # Finally, we build our project
-    && cargo build --release \
-    # After that we copy our binary to the project root (you need to adjust this to your project)
-    && cp target/release/mini-docker-rust . \
-    # Discard the target/ and ~/.cargo/ directory so it won't bloat our image
-    && rm -rf target/ ~/.cargo/ \
-    # As the final cleanup step we uninstall our virtual package
-    # This uninstalls cargo, rust and all dependencies that aren't needed anymore so they won't end up in the final image
-    && apk del --purge .build-rust
-# Finally, we configure our binary as entrypoint (you need to adjust this too)
-ENTRYPOINT ["./mini-docker-rust"]
-```
+See [Dockerfile](Dockerfile).