Dockerize your Scala application

Dockerizing a Scala application is pretty easy.

The first concern is creating a fat jar. Now we all come from different backgrounds including maven/gradle and different plugins that handle this issue.
If you use sbt the way to go is to use the sbt-assembly plugin.

To use it we should add it to our project/plugins.sbt file. If the file does not exist create it.

logLevel := Level.Warn

addSbtPlugin("com.eed3si9n" % "sbt-assembly" % "0.14.6")

So by executing

sbt clean assembly

We will end up with a fat jar located at the target/scala-**/**.jar path.

Now the easy part is putting our application inside docker, thus a Dockerfile is needed.

We will use the openjdk alpine as a base image.

FROM openjdk:8-jre-alpine

ADD target/scala-**/your-fat-jar app.jar

ENTRYPOINT ["java","-jar","/app.jar"]

The above approach works ok and gives the control needed to customize your build process.
For a more bootstraping experience you can use the sbt native packager.

All you need to do is to add the plugin to project/plugins.sbt file.

logLevel := Level.Warn

addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.3.4")

Then we specify the main class of our application and enable the Java and Docker plugins from the native packager at the build.sbt file.

mainClass in Compile := Some("your.package.MainClass")

enablePlugins(JavaAppPackaging)
enablePlugins(DockerPlugin)

The next step is to issue the sbt command.

sbt docker:publishLocal

This command will build your application, include the binaries needed to the jar, containerize your application and publish it to your local maven repo.

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