Gradle dependency caching during docker multi stage build?

Question

I have the following Dockerfile

FROM gradle:jdk13 AS appbuild
WORKDIR "/home/gradle/"
COPY --chown=gradle:gradle "./build.gradle" "/home/gradle/"
RUN gradle dependencies
COPY --chown=gradle:gradle "./src/" "/home/gradle/src/"
RUN gradle build --info

FROM openjdk:13
ENV LANG en_US.UTF-8
COPY --from=appbuild "/home/gradle/build/libs/frontend.jar" "/frontend.jar"
CMD ["java", "-jar", "-Dspring.profiles.active=default", "/frontend.jar"]

My aim is to prevent gradle from downloading the dependencies every time I build a docker image.

The command gradle dependencies downloads all the required java libraries in case they are missing.

Before the first gradle dependencies command I only copied the build.gradle in order to only download the dependencies and cache them.

When I run the gradle build command, why does it want to download all the files again? They are already present in one of the layers.

I have tried with RUN gradle clean build --info || return 0 instead of gradle dependencies, all the same.

Answer 1

The GRADLE_USER_HOME environment variable isn't set by default. You'll need to explicitly set it, and then copy over the downloaded dependencies in the next stage.

FROM gradle:jdk13 AS cache
WORKDIR /app
ENV GRADLE_USER_HOME /cache
COPY build.gradle gradle.properties settings.gradle ./
RUN gradle --no-daemon build --stacktrace

FROM gradle:jdk13 AS builder
WORKDIR /app
COPY --from=cache /cache /home/gradle/.gradle
COPY src/ src/
RUN gradle --no-daemon build --stacktrace

FROM openjdk:jre-alpine
WORKDIR /app
RUN apk --no-cache add curl
COPY --from=builder /app/build/libs/frontend.jar /frontend.jar
ENV PORT 80
EXPOSE 80
HEALTHCHECK --timeout=5s --start-period=5s --retries=1 \
    CMD curl -f http://localhost:$PORT/health_check
CMD ["java", "-jar", "-Dspring.profiles.active=default", "/frontend.jar"]

Here's my original Dockerfile. I've modified it for yours, but haven't tested it, so you can refer to the original if you're in doubt.