Multistage Docker Builds for Scala Applications

The following Dockerfile gives an example of a multistage build that runs sbt in a builder container. This means that users don’t need to install Scala tooling on their machines in order to build the project. To optimise build times, I cache dependencies first by running sbt update in a precursor step to sbt stage.

FROM hseeberger/scala-sbt:8u181_2.12.7_1.2.6 as builder
WORKDIR /build
# Cache dependencies first
COPY project project
COPY build.sbt .
RUN sbt update
# Then build
COPY . .
RUN sbt stage
# Download Geonames file
RUN wget
RUN unzip

FROM openjdk:8u181-jre-slim
COPY --from=builder /build/target/universal/stage/. .
COPY --from=builder /build/cities500.txt .
ENV PLACES_FILE_PATH=/app/cities500.txt
RUN mv bin/$(ls bin | grep -v .bat) bin/start
CMD ["./bin/start"]

The final image only has the JRE, and no build tools.

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