How would I create docker container of Gradle application? - docker

Question

I have a gradle spark application that needs to be used with docker to create a container. I am new to docker and I am having a hard time setting up Dockerfile.
In Dockerfile I tried executing build.gradle and running Main.java.
# Start with a base image containing Java runtime
FROM gradle:jdk10 as builder
COPY --chown=gradle:gradle . /home/gradle/src
WORKDIR /home/gradle/src
RUN gradle build
FROM openjdk:10-jre-slim
COPY ./ /tmp/
CMD ["cd tmp/src/main/java/Empowering/"]
CMD ["javac Main.java"]
EXPOSE 8080

Answer 1

For your runtime container, you shouldn't be using javac. Gradle is doing the build for you. So, you'll only need to worry about running what Gradle is producing. Additionally, you want to make sure that you're properly copying the stuff being built by your builder.
I don't know what type of application you are running and what you're Gradle configuration looks like so I'm going to have to make some assumptions here.
I would highly suggest that you utilize the application plugin if you're generating a web application. If that's the case the installDist will put everything you need into the build/install folder. Once that's in place, you can simply use the generated shell script for your CMD/ENTRYPOINT
For Example:
# Start with a base image containing Java runtime
FROM gradle:jdk10 as builder
COPY --chown=gradle:gradle . /home/gradle/src
WORKDIR /home/gradle/src
RUN gradle installDist
FROM openjdk:10-jre-slim
EXPOSE 8080
COPY --from=builder /home/gradle/src/build/install/<app name>/ /app/
WORKDIR /app
CMD ["bin/<app name>"]
If you're packaging as a jar, you can just simply copy the jar generated by the build/ fat jar task in the builder then run that
# Start with a base image containing Java runtime
FROM gradle:jdk10 as builder
COPY --chown=gradle:gradle . /home/gradle/src
WORKDIR /home/gradle/src
RUN gradle build
FROM openjdk:10-jre-slim
EXPOSE 8080
COPY --from=builder /home/gradle/src/build/<jar output path>/<app name>.jar /app/
WORKDIR /app
CMD ["java -jar <app name>.jar"]