Changing the JVM in spring-boot:build-image

#springbootmavenplugin #springboot #buildpack #docker

The spring-boot-maven-plugin can create an OCI image from a jar or war file using Cloud Native Buildpacks.

By default it uses a buildpack called paketo-buildpacks/bellsoft-liberica which is based on Bellsoft Liberica JDK.

The list of all Java buildpacks is available in Paketo Buildpacks Reference.

To choose another JVM in spring-boot-maven-plugin, first you need to find the buildpacks that are used by default. Run mvn spring-boot:build-image and look for something like this:

[INFO]     [creator]     ===> DETECTING
[INFO]     [creator]     6 of 26 buildpacks participating
[INFO]     [creator]     paketo-buildpacks/ca-certificates   3.6.1
[INFO]     [creator]     paketo-buildpacks/bellsoft-liberica 10.1.0
[INFO]     [creator]     paketo-buildpacks/syft              1.27.0
[INFO]     [creator]     paketo-buildpacks/executable-jar    6.6.3
[INFO]     [creator]     paketo-buildpacks/dist-zip          5.5.2
[INFO]     [creator]     paketo-buildpacks/spring-boot       5.23.0

That´s the list of buildpacks being used. We need to change Bellsoft Liberica to the desired JVM.

So, to use Microsoft OpenJDK, copy the buildpacks from above, but change paketo-buildpacks/bellsoft-liberica to gcr.io/paketo-buildpacks/microsoft-openjdk. The pom.xml should be:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <image>
            <buildpacks>
                <buildpack>paketo-buildpacks/ca-certificates</buildpack>
                <buildpack>gcr.io/paketo-buildpacks/microsoft-openjdk</buildpack>
                <buildpack>paketo-buildpacks/syft</buildpack>
                <buildpack>paketo-buildpacks/executable-jar</buildpack>
                <buildpack>paketo-buildpacks/dist-zip</buildpack>
                <buildpack>paketo-buildpacks/spring-boot</buildpack>
            </buildpacks>
        </image>
    </configuration>
</plugin>

Now, run mvn spring-boot:build-image and verify that Microsoft OpenJDK is being used:

[INFO]     [creator]     Paketo Buildpack for Microsoft OpenJDK 3.0.1
[INFO]     [creator]       https://github.com/paketo-buildpacks/microsoft-openjdk
...
[INFO]     [creator]       Microsoft OpenJDK 17.0.6: Contributing to layer
[INFO]     [creator]         Downloading from https://aka.ms/download-jdk/microsoft-jdk-17.0.6-linux-x64.tar.gz