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Scala for Backend Engineering & Functional Programming · Lesson

Containerization with Docker

Learn to containerize your Scala applications using Docker for consistent environments and simplified deployment.

Containerization with Docker is a free Scala for Backend Engineering & Functional Programming lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Scala for Backend Engineering & Functional Programming learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Containerize Scala Apps?

When deploying Scala applications, ensuring a consistent environment across development, testing, and production can be challenging. This is where containerization comes in!

A container packages your application and all its dependencies (like the Java Virtual Machine, libraries, and configuration) into a single, isolated unit. This ensures it runs the same way, everywhere.

Docker: Images and Containers

Docker is the most popular platform for containerization. It uses two core concepts:

  • Docker Image: A lightweight, standalone, executable package that includes everything needed to run a piece of software, including the code, a runtime, system tools, system libraries, and settings. Think of it as a blueprint.
  • Docker Container: A runnable instance of a Docker image. When you run an image, it becomes a container. Containers are isolated from each other and from the host system.

Your First Docker Run

Let's try running a very basic Docker container. This command pulls the hello-world image (if not already present) and runs it as a container.

You'll see a message confirming Docker is working!

docker run hello-world

Our Simple Scala App

Before we containerize, let's create a minimal Scala application. This program will simply print a message to the console.

We'll package this into a Docker image soon!

object Main extends App {
  val message = "Hello from CoddyKit's Docker container!"
  println(message)
}

Blueprint: The Dockerfile

A Dockerfile is a text file that contains all the commands a user could call on the command line to assemble an image. It's like a recipe for building your Docker image.

Key instructions include:

  • FROM: Sets the base image.
  • WORKDIR: Sets the working directory.
  • COPY: Copies files into the image.
  • RUN: Executes commands during image build.
  • CMD: Specifies the command to run when the container starts.

Dockerfile: Build Stage for Scala

For Scala, we often use a multi-stage build. The first stage builds our application. We use an OpenJDK image with a full JDK to compile our Scala code.

# Stage 1: Build the Scala application
FROM adoptopenjdk/openjdk11:latest as builder
WORKDIR /app
COPY Main.scala .
RUN scalac Main.scala
RUN jar -cvf app.jar Main.class

Dockerfile: Runtime Stage for Scala

The second stage creates a much smaller image, containing only the JRE (Java Runtime Environment) and our compiled Scala application (the JAR file). This keeps the final image size minimal.

# Stage 2: Create a minimal runtime image
FROM adoptopenjdk/openjdk11:jre-hotspot
WORKDIR /app
COPY --from=builder /app/app.jar .
CMD ["java", "-jar", "app.jar"]

Complete Scala Dockerfile

Here's the full multi-stage Dockerfile for our Scala application. This file should be named Dockerfile and placed in the same directory as your Main.scala.

# Stage 1: Build the Scala application
FROM adoptopenjdk/openjdk11:latest as builder
WORKDIR /app
COPY Main.scala .
RUN scalac Main.scala
RUN jar -cvf app.jar Main.class

# Stage 2: Create a minimal runtime image
FROM adoptopenjdk/openjdk11:jre-hotspot
WORKDIR /app
COPY --from=builder /app/app.jar .
CMD ["java", "-jar", "app.jar"]

Building the Docker Image

Now that we have our Dockerfile and Main.scala, let's build the Docker image. The -t flag tags our image with a name (e.g., scala-hello) and . indicates the current directory is the build context.

docker build -t scala-hello .

Running Your Containerized Scala App

After the image is built, you can run your Scala application inside a Docker container using the docker run command. This will execute the CMD instruction defined in your Dockerfile.

docker run scala-hello

You should see "Hello from CoddyKit's Docker container!" printed to your console!

Check Your Knowledge

Test your understanding of Dockerfiles.

Recap: Containerizing Scala

You've successfully learned the basics of containerizing a Scala application with Docker!

  • Docker Images are blueprints, Containers are runnable instances.
  • A Dockerfile is a recipe for building your image.
  • Multi-stage builds help create small, efficient images for Scala apps.
  • Commands like docker build and docker run manage your images and containers.

This knowledge is crucial for deploying Scala microservices consistently and reliably.

Frequently asked questions

Is the “Containerization with Docker” lesson free?

Yes — the full text of “Containerization with Docker” is free to read here on the web, and the Scala for Backend Engineering & Functional Programming course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Scala for Backend Engineering & Functional Programming course, upgrade to CoddyKit PRO.

What will I learn in “Containerization with Docker”?

Learn to containerize your Scala applications using Docker for consistent environments and simplified deployment. You practise Scala for Backend Engineering & Functional Programming with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Scala for Backend Engineering & Functional Programming?

No prior experience is required. Scala for Backend Engineering & Functional Programming on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Containerization with Docker” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Scala for Backend Engineering & Functional Programming lesson?

Yes. Every Scala for Backend Engineering & Functional Programming lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Designing Scala Microservices
  2. Containerization with Docker
  3. Cloud Deployment Strategies
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