5.1 Example Application

App - the standard way

Using example Spring Boot app

git clone https://github.com/spring-guides/gs-spring-boot.git
cd gs-spring-boot/initial

Create the .dockerignore file inside gs-spring-boot/initial with following content:

Containerfile*

This should make builds faster. Changes in Containerfiles have no impact on build context and caching.

Test base image candidate and get infos:

docker run -ti docker.io/eclipse-temurin:21-jdk-ubi9-minimal /bin/bash

# execute inside the image:

# user
whoami

# location
pwd

# java version
java -version

As we see, this image runs as user root inside root / and has java version 21.

Create the Containerfile.jdk file inside gs-spring-boot/initial with following content:

FROM docker.io/eclipse-temurin:21-jdk-ubi9-minimal AS build
# user: root!
COPY . .
RUN ./gradlew build

FROM docker.io/eclipse-temurin:21-jre-ubi9-minimal
COPY --from=build /build/libs/spring-boot-0.0.1-SNAPSHOT.jar /
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "/spring-boot-0.0.1-SNAPSHOT.jar"]

This is a multistage build using a JDK to build the app and a JRE container to run it.

Build image (includes app build):

docker build -t my-spring-jdk -f Containerfile.jdk .

Attention: Clean local build and .gradle files if you encounter file permission problems.

Test app inside container:

docker run -ti --entrypoint /bin/bash my-spring-jdk
java -jar /spring-boot-0.0.1-SNAPSHOT.jar

Exit with ctrl+d

Run container:

docker run -p 8080:8080 my-spring-jdk

Open your browser at http://localhost:8080/

You should see: Greetings from Spring Boot!

Stop container with ctrl+c