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.
| Published on Java Code Geeks with permission by Emmanouil Gkatziouras, partner at our JCG program. See the original article here: Dockerize your Scala application Opinions expressed by Java Code Geeks contributors are their own. |
