Document how to generate a native image from Spring Boot executable JAR

[sergey-morenets]

Hi

We would like to generate native image by native-image utility in Dockerfile:

native-image -jar custom-spring-boot.jar

But it seems that in generated fat jar META-INF/native-image folder is not root as described in GraalVM documentation:
https://docs.oracle.com/en/graalvm/enterprise/20/docs/reference-manual/native-image/BuildConfiguration/

It's located under BOOT-INF/classes and native-image is unable to detect it. Whereas Micronaut (and Micronaut plugins) create META-INF/native-image in the root folder in the generated jar.
So the question is: is it possible to generate GraalVM native image (using plugin or by another approach)?

[sdeleuze]

native-image does not recognize Spring Boot executable JAR format, and we currently provide 2 ways of creating native images via build plugins as documented here.

That said, native image creation being designed to be run on CI/CD platform and given the fact that most containers are CPU architecture specific, I see some value in providing the capability to turn a Spring Boot executable JAR to a native image. Just not sure how we could/should implement that.

Any thoughts @bclozel @snicoll @aclement ?

[sdeleuze]

Maybe pack already allows to do that via https://github.com/paketo-buildpacks/native-image ?

[sergey-morenets]

native-image does not recognize Spring Boot executable JAR format, and we currently provide 2 ways of creating native images via build plugins as documented here.

That said, native image creation being designed to be run on CI/CD platform and given the fact that most containers are CPU architecture specific, I see some value in providing the capability to turn a Spring Boot executable JAR to a native image. Just not sure how we could/should implement that.

Any thoughts @bclozel @snicoll @aclement ?

Yes, that's correct. But spring-boot:build-image goal generates OCI image with native image application. Sometimes I want to build OCI (Docker) image by myself. In that case I just need a goal to compile native image but Spring Boot plugin doesn't support that now.

[sdeleuze]

For that you can use native-image-maven-plugin documented here.

[sergey-morenets]

@sdeleuze

Yes, but I will get fallback image, because unfortunately Native Image Builder doesn't recognize and support Spring Boot JAR Layout. So I will need JDK/JRE to run it.

[sdeleuze]

I mean from sources not the executable JAR (btw we disable fallback in Spring Native).
From executable JAR, you should be able to generate a container image (follow #738). I am discussing with the GraalVM team if we should or not supporting generating a native image from a Spring Boot executable JAR, I will reopen this issue if we decide to support that.