Contrib module for building docker images

3 files changed, 121 insertions, 0 deletions

diff --git a/build.sc b/build.sc
index bc693f1c..4d9133d0 100755
--- a/build.sc
+++ b/build.sc
@@ -306,6 +306,10 @@ object contrib extends MillModule {
     def moduleDeps = Seq(scalalib)
     def ivyDeps = Agg(ivy"org.flywaydb:flyway-core:5.2.4")
   }
+
+  object docker extends MillModule {
+    def moduleDeps = Seq(scalalib)
+  }
 }
 
 
diff --git a/contrib/docker/src/DockerModule.scala b/contrib/docker/src/DockerModule.scala
new file mode 100644
index 00000000..bbf4d926
--- /dev/null
+++ b/contrib/docker/src/DockerModule.scala
@@ -0,0 +1,73 @@
+import mill.T
+import mill.scalalib.JavaModule
+import os.Shellable.IterableShellable
+
+import scala.collection.immutable._
+
+trait DockerModule { outer: JavaModule =>
+
+  trait DockerConfig extends mill.Module {
+    /**
+      * Tags that should be applied to the built image
+      * In the standard registry/repository:tag format
+      */
+    def tags: T[Seq[String]] = T(List(outer.artifactName()))
+    def labels: T[Map[String, String]] = Map.empty[String, String]
+    def baseImage: T[String] = "gcr.io/distroless/java:latest"
+    def pullBaseImage: T[Boolean] = T(baseImage().endsWith(":latest"))
+    private def baseImageCacheBuster: T[(Boolean, Double)] = T.input {
+      val pull = pullBaseImage()
+      if(pull) (pull, Math.random()) else (pull, 0d)
+    }
+
+    def dockerfile: T[String] = T {
+      val jarName = assembly().path.last
+      val labelRhs = labels()
+        .map { case (k, v) =>
+          val lineBrokenValue = v
+            .replace("\r\n", "\\\r\n")
+            .replace("\n", "\\\n")
+            .replace("\r", "\\\r")
+          s""""$k"="$lineBrokenValue""""
+        }
+        .mkString(" ")
+
+      val labelLine = if(labels().isEmpty) "" else s"LABEL $labelRhs"
+
+      s"""
+         |FROM ${baseImage()}
+         |$labelLine
+         |COPY $jarName /$jarName
+         |ENTRYPOINT ["java", "-jar", "/$jarName"]
+      """.stripMargin
+    }
+
+    final def build = T {
+      val dest = T.ctx().dest
+
+      val asmPath = outer.assembly().path
+      os.copy(asmPath, dest / asmPath.last)
+
+      os.write(dest / "Dockerfile", dockerfile())
+
+      val log = T.ctx().log
+
+      val tagArgs = tags().flatMap(t => List("-t", t))
+
+      val (pull, _) = baseImageCacheBuster()
+      val pullLatestBase = IterableShellable(if(pull) Some("--pull") else None)
+
+      val result = os
+        .proc("docker", "build", tagArgs, pullLatestBase, dest)
+        .call(stdout = os.Inherit, stderr = os.Inherit)
+
+      log.info(s"Docker build completed ${if(result.exitCode == 0) "successfully" else "unsuccessfully"} with ${result.exitCode}")
+      tags()
+    }
+
+    final def push() = T.command {
+      val tags = build()
+      tags.foreach(t => os.proc("docker", "push", t).call(stdout = os.Inherit, stderr = os.Inherit))
+    }
+  }
+}
\ No newline at end of file
diff --git a/docs/pages/9 - Contrib Modules.md b/docs/pages/9 - Contrib Modules.md
index 1b9b55fa..9adddcc5 100644
--- a/docs/pages/9 - Contrib Modules.md
+++ b/docs/pages/9 - Contrib Modules.md
@@ -38,6 +38,50 @@ object project extends BuildInfo {
 * `def buildInfoPackageName: Option[String]`, default: `None`
   The package name of the object.
   
+### Docker
+
+Automatically build docker images from your mill project.
+
+Requires the docker CLI to be installed.
+
+In the simplest configuration just extend `DockerModule` and declare a `DockerConfig` object.
+
+```scala
+import mill._, scalalib._
+
+import ivy`com.lihaoyi::mill-contrib-docker:VERSION`
+import contrib.docker.DockerModule
+
+object foo extends JavaModule with DockerModule {
+  object docker extends DockerConfig
+}
+```
+
+Then
+
+```
+$ mill foo.docker.build
+$ docker run foo
+```
+
+#### Configuration
+
+Configure the image by overriding tasks in the `DockerConfig` object
+
+```scala
+object docker extends DockerConfig {
+  // Override tags to set the output image name
+  def tags = List("aws_account_id.dkr.ecr.region.amazonaws.com/hello-repository")
+  
+  def baseImage = "openjdk:11"
+  
+  // Configure whether the docker build should check the remote registry for a new version of the base image before building.
+  // By default this is true if the base image is using a latest tag
+  def pullBaseImage = true
+}
+```
+
+Run mill in interactive mode to see the docker client output, like `mill -i foo.docker.build`.
   
 ### Flyway