Build Spring Boot fat JAR using JIB - jib

Question

I have a multi-modules project from which I build spring boot apps using Jib. I understood that fat JAR into container prevents building image efficiently (see) but one particular module needs to be packaged into a fat JAR file. As I would like to keep the same building tool for the whole multi-modules project, is it possible to package fat jar using Jib?
I already tried the repackage goal
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>2.3.5.RELEASE</version>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
that is packaging the app such as
app
├── classpath
│   └── import-metadata-service-0.0.1-SNAPSHOT.original.jar
└── libs
├── HdrHistogram-2.1.12.jar
├── LatencyUtils-2.0.3.jar
├── apache-jena-libs-3.13.0.pom
...

Answer 1

Yes, it is possible to put a fat jar on to the container image using Jib. Please use "containerizingMode" configuration option of Jib:
<plugin>
<groupId>com.google.cloud.tools</groupId>
<artifactId>jib-maven-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>build</goal>
</goals>
</execution>
</executions>
<configuration>
<containerizingMode>packaged<containerizingMode>
</configuration>
</plugin>
Please refer https://github.com/GoogleContainerTools/jib/tree/master/jib-maven-plugin#extended-usage for a full set of Jib configuration option.

Answer 2

In case someone is stumbling over this: I have a similar usecase where I want to take advantage of jib (Dockerfile-less + can be used without docker daemon), but I currently cannot turn away from fat jars for other reasons.
Based on Chanseok comments (under the question), I came up with following, which will:
drop any layers added by jib
add the fatjar (by default in target/${build.finalName}.jar) into its own layer
overwrite entrypoint to execute "java -jar ..." instead of regular entrypoint pointing to your Main
Jib is called explicitly and not bound to lifecycle (at least in my sample), so it would have to be called explicitly with following mvn package jib:dockerBuild (or ... jib:build for a docker-daemon-less build)
using dive, you see that only one layer was added and that it is fairly large (== fat jar)
Sources: https://gitter.im/google/jib?at=5fad68c5d37a1a13d6a12174 + https://github.com/GoogleContainerTools/jib/tree/master/jib-maven-plugin#extradirectories-object
That sample works at least with spring boot 2.4.X
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<groupId>com.google.cloud.tools</groupId>
<artifactId>jib-maven-plugin</artifactId>
<version>3.0.0</version>
<dependencies>
<dependency>
<groupId>com.google.cloud.tools</groupId>
<artifactId>jib-layer-filter-extension-maven</artifactId>
<version>0.2.0</version>
</dependency>
</dependencies>
<configuration>
<container>
<entrypoint>java,-jar,/app/${project.build.finalName}.jar</entrypoint>
</container>
<extraDirectories>
<paths>
<path>
<from>target/</from>
<includes>*.jar</includes>
<into>/app</into>
</path>
</paths>
</extraDirectories>
<pluginExtensions>
<pluginExtension>
<implementation>com.google.cloud.tools.jib.maven.extension.layerfilter.JibLayerFilterExtension</implementation>
<configuration implementation="com.google.cloud.tools.jib.maven.extension.layerfilter.Configuration">
<filters>
<filter>
<!-- exclude all jib layers, which is basically anything in /app -->
<glob>/app/**</glob>
</filter>
<filter>
<!-- this is our fat jar, this should be kept by adding it into its own layer -->
<glob>/app/${project.build.finalName}.jar</glob>
<toLayer>jib-custom-fatJar</toLayer>
</filter>
</filters>
</configuration>
</pluginExtension>
</pluginExtensions>
</configuration>
</plugin>
</plugins>
</build>