Building Spring Boot Docker Image
Table of Contents
Pre-Requirements
- Developer Environment ready with Docker, JDK, IDE
- A Java Spring Boot Project with a h2 in-memory DB
- Docker Hub account
Create Docker File
Create a Dockerfile with the following content:
FROM openjdk:11-jre-slim
ENV JAVA_OPTS " -Xms512m -Xmx512m -Djava.security.egd=file:///dev/./urandom"
WORKDIR application
COPY target/myapp-0.0.1-SNAPSHOT.jar ./
ENTRYPOINT ["java", "-jar", "myapp-0.0.1-SNAPSHOT.jar"]
Make sure the paths where the .jar files are stored match your environment.
Build and Run the Docker Image
Build the image with this command:
docker build -f ./src/main/Dockerfile -t myapp .
Run the image with this command:
docker run -p 8080:8080 -d myapp
The Spring Application-Context should now be loaded and started inside the container. You can verify this with the docker ps -a and docker logs -f <containername> commands.
Add Layer Tool in Maven
Make sure that you have enabled the Layer Tool with the following content in the pom.xml file:
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<layers>
<enabled>true</enabled>
<includeLayerTools>true</includeLayerTools>
</layers>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
Enabling the layer tool in a Java Spring project that runs in a Docker container can help reduce the size of the Docker image, improve the speed of deployment, and optimize resource usage.
Enable Multi-Stage Dockerfile
Create an example of a Multi-Stage Dockerfile:
FROM openjdk:11-jre-slim as builder
WORKDIR application
ADD target/myapp-0.0.1-SNAPSHOT.jar ./
RUN java -Djarmode=layertools -jar myapp-0.0.1-SNAPSHOT.jar extract
FROM openjdk:11-jre-slim
WORKDIR application
COPY --from=builder application/dependencies/ ./
COPY --from=builder application/spring-boot-loader/ ./
COPY --from=builder application/snapshot-dependencies/ ./
COPY --from=builder application/application/ ./
ENTRYPOINT ["java", "-Djava.security.egd=file:///dev/./urandom", "org.springframework.boot.loader.JarLauncher"]
Recreate the image with:
docker build -f ./src/main/docker/Dockerfile -t myapp .
Build the Docker Image with Maven
Add the Docker Maven plugin to your pom.xml:
<plugin>
<groupId>io.fabric8</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>0.42.1</version>
<configuration>
<verbose>true</verbose>
<images>
<image>
<name>yourdockeraccount/myapp</name>
<build>
<assembly>
<descriptorRef>artifact</descriptorRef>
</assembly>
<dockerFile>Dockerfile</dockerFile>
<tags>
<tag>latest</tag>
<tag>${project.version}</tag>
</tags>
</build>
</image>
</images>
</configuration>
</plugin>
Replace the artifact name myapp-0.0.1-SNAPSHOT.jar with ${project.build.finalName}.jar in the Dockerfile.
Build the Docker image with the Maven plugin using a dynamic version.
Push your Docker Image to Docker Hub
Build the image with:
mvn clean package docker:build docker:push