Dockerize gradle project

#1: Configure gradle to produce fat jar

Read -> this

#2: Writing Dockerfile

Stage 1: Cache dependencies

Use multi-stage docker build process to separate and cache the dependencies library

ARG BUILD_HOME=/home/gradle/app

FROM gradle:jdk17-alpine as cache
ARG BUILD_HOME
WORKDIR $BUILD_HOME
ENV GRADLE_USER_HOME /cache
COPY build.gradle gradle.properties settings.gradle ./
RUN gradle build --no-daemon --stacktrace

Above will produce a stage of docker build with all your project dependencies downloaded
and this wont be built again untill you change anything in above code.

Stage 2: Build your project

FROM gradle:jdk17-alpine as builder
ARG BUILD_HOME
WORKDIR $BUILD_HOME
COPY --from=cache /cache /home/gradle/.gradle
COPY . $BUILD_HOME/
RUN gradle --no-daemon clean build --stacktrace

In above, we copied the source code and did a clean gradle build.

Stage 3: Running the project

Separating this stage from the previous step allows us to produce a lighter image excluding source files etc.

FROM openjdk:17
ARG BUILD_HOME
WORKDIR $BUILD_HOME
COPY --from=builder $BUILD_HOME/build/libs/hello-api.jar app.jar
EXPOSE 80
ENTRYPOINT ["java","-jar","app.jar"]

#3. Building

Run below

docker build -t hello-api:latest .

---

So the final Dockerfile will look something like this

ARG BUILD_HOME=/home/gradle/app

FROM gradle:jdk17-alpine as cache
ARG BUILD_HOME
WORKDIR $BUILD_HOME
ENV GRADLE_USER_HOME /cache
COPY build.gradle gradle.properties settings.gradle ./
RUN gradle build --no-daemon --stacktrace

FROM gradle:jdk17-alpine as builder
ARG BUILD_HOME
WORKDIR $BUILD_HOME
COPY --from=cache /cache /home/gradle/.gradle
COPY . $BUILD_HOME/
RUN gradle --no-daemon clean build --stacktrace

FROM openjdk:17
ARG BUILD_HOME
WORKDIR $BUILD_HOME
COPY --from=builder $BUILD_HOME/build/libs/hello-api.jar app.jar
EXPOSE 80
ENTRYPOINT ["java","-jar","app.jar"]

FAQs

Q: What if I want to rebuild all stages i.e. not use cached stages?
A: use --no-cache like below

docker build --no-cache -t hello-api:latest .

Q: Why ARG declared before FROM statement at start of the file?
A: Read --> this