Cross-compilation with the JLink & Docker plugins

[demming]

Observed and desired behavior

Using both the JLink an the Docker plugins, when developing on a Mac machine, I'd like to get a Docker image that would run on a Linux machine on a CPU architecture determined by the JDK base image, from which JLink would cherry-pick the required modules.

Right now docker:publishLocal builds the package locally outside Docker, and then injects the resulting package into the Docker image with the JDK/JRE base image for the target platform. This works fine. And I greatly appreciate it. However, the resulting container image is typically relatively large. I'd like to minimize the target JDK/JRE. This issue had come up already in #1449.

Specifically, running moduleName / docker:publishLocal performs the JLink instructions (with a lot of missing transitive dependencies, but that's a different story that I need to investigate more thoroughly) against the local JDK given by javaHome0 in JlinkPlugin.scala#L52.

I need the JLink plugin to run inside a container against the target JDK prior to the copying stage0.

I imagine there should be a way for cross-compiling with JLink to either

• provide the path to another local JDK (which isn't good for replication), or

• add a pre-stage to the resulting Dockerfile that would run either

  • the entire sbt build, or
  • the JLink plugin

  against the target JDK, and then use that stage rather than the baseline image.

At least I can extract the JLink parameter values and pass them on to modified Dockerfile instructions in my build.sbt but this would get all messy with a larger CI configuration and doesn't seem ready for full build automation.

Running the entire sbt workflow inside a container would solve this issue but it would break a lot of tooling and complicate the matters, for example IntelliJ IDEA didn't support it in its 2019 versions.

If there's some simple work-around please point me in the right direction.

Information

• sbt-native-packager: 1.9.4
• sbt: 1.6.1
• Build system: macOS aarch64 M1 (local) + Debian (amd64, arm32v7l, arm64v8 / aarch64) targets
• Plugins: Docker & JLink
• Build tool: Docker version 20.10.12
• Target systems: macOS on aarch64 & amd64 (local) and Linux on amd64 & arm32v7l & arm64v8 (remote Docker machines)