Packaging an Akka-http Application using SBT and Docker: Simple Example

This post will walk you through setting up a minimal akka-http example (including Json marshalling/unmarshalling, accessing external resources and other goodies) and making it ready for packaging with docker.

We'll be using sbt-native-packager, which you can use not only to create Docker containers but a variety of other package formats (e.g. deb, rpm, msi and zip).

TL;DR: See sample project here: akka-http-docker-minimal-seed

Prerequisites: Docker and SBT

• Docker Installation Instructions for all supported Platforms

• SBT Download instructions

Clone the sample app from github

$ git clone https://github.com/queirozfcom/akka-http-docker-minimal-seed.git

Examining the files

I won't go into the details of how to put together an akka-http application here; the code is heavily commented so you should be able to pick up what you should do from the example.

There are a couple of files that you need to take special notice of:

• build.sbt

  The first line is used to configure what type of package you want. For Docker, use JavaAppPackaging (even though this is a Scala project!):

  lazy val root = (project in file(".")).enablePlugins(JavaAppPackaging)
  

  This is where you set the Docker container name:

  packageName in Docker := "akka-http-docker-minimal-seed"
  

  The following line is needed to inform Docker we want open a port on the container so we can access from outside (there may be more than one)

  dockerExposedPorts := Seq(5000)
  

• project/plugins.sbt

  The following line

  addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "1.1.1")
  

  adds the plugin to sbt.

Packaging and Running the Project

To package the app, you need to run a single command:

$ sbt docker:publishLocal

This will package your akka-http app into a Docker container and make it available for running with Docker.

After generating the container (step above), run the container:

$ docker run -dit -p 5000:5000 --name akka-minimal-seed akka-http-docker-minimal-seed:1.0

You will get a response like this:

$ docker run -dit -p 5000:5000 --name akka-minimal-seed akka-http-docker-minimal-seed:1.0
6c3ceda8b0a4dc67633c577bb57dd949e17afbc101fd1b190c2e67efba9c9b7f

This will run in the background (because of the -d switch) so you won't see

Testing the app

• Open address on a web browser: http://localhost:5000/healthcheck

• To test using Postman, use this link:

  

Stop the container

To stop the container, run:

$ docker stop akka-minimal-seed

If you prefer to remove the container rather than just stop it, just run docker rm instead of docker stop.

Troubleshooting: "Cannot connect to the Docker daemon. Is the docker daemon running on this host?"

• SO Answer: Docker-Can't connect to Docker Daemon