SBT Build Environment Dependent Docker Image

build.sbt

lazy val deploymentSettings = settingKey[DeploymentSettings]("My environment")

lazy val commonSettings = Seq(
  name := "test-docker",
  version := "0.1",
  scalaVersion := "2.12.3",
  imageNames in docker := Seq(
    ImageName(s"${deploymentSettings.value.dockerRegistry}/test-image")),
  dockerfile in docker := {
    new Dockerfile {
      from("anapsix/alpine-java")
      entryPoint("java", "-version")
    }
  }
)

lazy val root = (project in file("."))
  .enablePlugins(BuildEnvPlugin, DockerPlugin)
  .settings(commonSettings)

BuildEnvPlugin.scala

import BuildEnvPlugin.autoImport.BuildEnv
import com.sun.xml.internal.ws.api.config.management.policy.ManagementAssertion.Setting
import sbt.PluginTrigger.AllRequirements
import sbt.{AutoPlugin, Def, PluginTrigger, Plugins}
import sbtdocker.DockerPlugin
import sbt._
import sbt.Keys._

object BuildEnvPlugin extends AutoPlugin {
  override def trigger: PluginTrigger = AllRequirements

  override def requires: Plugins = DockerPlugin

  object autoImport {
    object BuildEnv extends Enumeration {
      val Production, Stage, Test, Developement = Value
    }

    val buildEnv: SettingKey[BuildEnv.Value] =
      settingKey[BuildEnv.Value]("the current build environment")
    val deploymentSettings: SettingKey[DeploymentSettings] =
      settingKey[DeploymentSettings]("Deployment settings")
  }

  override def projectSettings: Seq[Def.Setting[_]] = {
    import autoImport._

    Seq(
      buildEnv := sys.props
        .get("env")
        .orElse(sys.env.get("BUILD_ENV"))
        .flatMap {
          case "prod"  => Some(BuildEnv.Production)
          case "stage" => Some(BuildEnv.Stage)
          case "test"  => Some(BuildEnv.Test)
          case "dev"   => Some(BuildEnv.Developement)
          case _       => None
        }
        .getOrElse(BuildEnv.Developement),
      deploymentSettings := {
        buildEnv.value match {
          case BuildEnv.Production => ProductionDeploymentSettings
          case _                   => LocalDeploymentSettings
        }
      },
      onLoadMessage := {
        val defaultMessage = onLoadMessage.value
        val env = buildEnv.value
        s"""|$defaultMessage
            |Running in build environment: $env""".stripMargin
      }
    )
  }
}

DeploymentSettings.scala

trait DeploymentSettings {
  var dockerRegistry: String
  var imageName: String = "hello"
  var dockerImages: Seq[ImageName] = Seq(ImageName(s"$dockerRegistry/$imageName"))
}

object LocalDeploymentSettings extends DeploymentSettings {
  override var dockerRegistry = "eu.gcr.io/staging"
}

object ProductionDeploymentSettings extends DeploymentSettings {
  override var dockerRegistry = "eu.gcr.io/production"
}