Dockerfile

The last peice we need to take care of in order have our pipleline fully function is a Dockerfile.

Dockerfile

When you run the docker command, Docker uses this file to build the image itself. The Dockerfile is essentially the build instructions to build the image.

At the top level of your project folder, create a new file called Dockerfile and copy & paste the following content into it:

# For Java 11, try this

FROM adoptopenjdk/openjdk11:latest AS build

ARG JAR_FILE=workspace/build/libs/ci-helloworld-1.0-SNAPSHOT.jar

RUN mkdir -p /workspace

COPY build.gradle /workspace

COPY gradlew /workspace

COPY settings.gradle /workspace

COPY gradle /workspace/gradle

COPY src /workspace/src

WORKDIR /workspace

RUN chmod a+x gradlew

RUN ./gradlew build

FROM adoptopenjdk/openjdk11:latest

COPY --from=build ${JAR_FILE} app.jar

EXPOSE 6379

ENTRYPOINT ["java","-jar","app.jar"]

This Dockerfile configuration will create a container image from the Gradle project. The FROM instruction initialises a new build stage and sets the base image as openjdk11:latest for subsequent instructions. ARG create a variable named JAR_FILE with the given value. RUN mkdir -p /workspace creates a folder called workspace. WORKDIR /workspace sets the working directory to /workspace for any RUN, ENTRYPOINT or COPY that follows in the Dockerfile. The build.gradle, settings.gradle, gradew files along with the src directory is then copied to /workspace. chmod a+x gradlew makes sure gradlew is executable. After that the shell command ./gradlew build is ran to build the jar file.

FROM adoptopenjdk/openjdk11:latest sets the JDK as the base image. We then copy the jar we created in the build phase into a new jar file called app.jar. EXPOSE 6379 informs Docker that the container listens on port 6379. The last bit, ENTRYPOINT [“java”,”-jar”,”app.jar”] tells the container to run java -jar app.jar once the container starts up.

add, commit, push

Do not forget to git add, commit and push your new Dockerfile.