Assembly included in image seems to be incorrect

[tetebueno]

Description

When configuring a project with a .jar artifact to include the artifact (as the descriptorRef) assembly in the final image includes a docker-build file instead. I imagine this has to do with a misconfiguration or misunderstanding of how to configure the plugin, but, having checked resources such as issues and tutorials, I still can't fix this.

So I have a Spring Boot project which builds a jar artifact with the application, I'm trying to add the configured plugin so the artifact is an image with the generated jar inside. The pom.xml file looks like this:

...
    <groupId>a.group</groupId>
    <artifactId>theId</artifactId>
    <version>0.1.0</version>
    <packaging>docker-build</packaging>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.7</version>
        <relativePath/>
    </parent>
...
    <build>
...
            <plugin>
                <groupId>io.fabric8</groupId>
                <artifactId>docker-maven-plugin</artifactId>
                <version>0.40.3</version>
                <extensions>true</extensions>
                <configuration>
                    <images>
                        <image>
                            <name>${project.artifactId}:${project.version}</name>
                            <build>
                                <from>openjdk:11-jre-slim</from>
                                <assembly>
                                    <descriptorRef>artifact</descriptorRef>
                                    <targetDir>/opt/${project.artifactId}</targetDir>
                                </assembly>
                                <entryPoint>java -jar /opt/${project.artifactId}/${project.artifactId}-${project.version}.jar</entryPoint>
                            </build>
                        </image>
                    </images>
                </configuration>
            </plugin>
        </plugins>
    </build>
...

After the image is built with the following command:

$ mvn clean install

I run a container using the image and I get this artifact:

$ ls /opt/theId
theId-0.1.0.docker-build

I was expecting the extension to be .jar, but I'm sure I'm missing something related to the packaging defined.

Thanks!

Info

• docker-maven-plugin version : 0.40.3
• Maven version (mvn -v) :

Apache Maven 3.8.6 (84538c9988a25aec085021c365c560670ad80f63)
Maven hame: /opt/maven
Java version: 11.0.16, vendor: Ubuntu, runtime: /usr/lib/jvm/java-11-openjdk-amd64
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "4.15.0-193-generic", arch: "amd64", family: "unix"

• Docker version :18.09.3, build 77pa1f4
• If it's a bug, how to reproduce : N/A
• If it's a feature request, what is your use case : N/A
• Sample project : N/A

[tetebueno]

Still waiting for an answer but, in case anyone bumped into this, as workaround, we're executing:

$ mvn package docker:build

With the default Maven project packaging (jar) and no <extensions> tag enabled.