Build Spring Boot fat JAR using 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>