Scala, docker - how to set mainClass in multimodule application using sbt-native-packager?

I have created a multimodule, sbt project in Scala. For now it is:

main project (main-service) with build.sbt file
http module with Main class

In my sbt file I have:

lazy val root = (project in file("."))
  .aggregate(http)
  .settings(
    dockerBaseImage := "openjdk:jre-alpine",
    name := "main-service",
    libraryDependencies ++= Seq(

    )
  )
  .enablePlugins(JavaAppPackaging)
  .enablePlugins(DockerPlugin)
  .enablePlugins(AshScriptPlugin)

lazy val http = (project in file("http"))
  .settings(
    mainClass in Compile := Some("Main"),
    name := "main-http",
    libraryDependencies ++= Seq(    
    ))

As you can see, I want to run it with docker. Image of this project is created well, but when I made docker run then I got an error:

docker: Error response from daemon: OCI runtime create failed: container_linux.go:345: starting container process caused "exec: \"/opt/docker/bin/main-service\": stat /opt/docker/bin/main-service: no such file or directory": unknown.

I think the problem could be with mainClass line. I have my Main class in main-http/src/main/scala directory, but it looks like docker does not see it.

How should I move this Main class or change path to it and run it correctly?

Solution

If you want to keep the main class in http subproject, you need to move the plugins to this project too as following.

lazy val root = (project in file("."))
  .aggregate(http)
  .settings(name := "main-service")

lazy val http = (project in file("http"))
  .settings(
    mainClass in Compile := Some("Main"),
    dockerBaseImage := "openjdk:jre-alpine",
    name := "main-http",
    libraryDependencies ++= Seq()
  )
  .enablePlugins(JavaAppPackaging)
  .enablePlugins(DockerPlugin)
  .enablePlugins(AshScriptPlugin)

The plugins must be enabled at the project where the Main class is located.

To build a docker image, do

sbt http/docker:publishLocal