Exercises for Containerisation Workshop

Create Dockerfiles for these applications

Pre-requisites

• Install Docker Desktop or Rancher Desktop (OSS)
• Make sure docker -v works from your terminal.

Assignment

1. Create a Dockerfile for each app, starting with the lang/tech you feel most comfortable with.
2. Your Dockerfile must be split into a build stage and a runner/app stage.
3. It must start the application when using docker run

Useful commands

Building

• Build: docker build <./dir/with/dockerfile> -t <image-tag> (assumes Dockerfile dir is also build context)
  • Serialized: DOCKER_BUILDKIT=0 docker build ... (debug each layer/cmd, by using printed sha as image-tag)
• Re-tag: docker tag <image-tag> <new-image-tag>
• Images & their sizes: docker images

Running

• What's running? docker ps
• Run: docker run <image-tag> (runs interactively until done or ctrl+c)
• Keep running: docker run --detached <image-tag> (runs in background until done)
• Debug: docker run -it --entrypoint /bin/bash <image-tag>

1. ubuntu-debugger

Simple image that extends Ubuntu 24.04 distro with some extra network debugging tools. Useful to understand base-images and layering

TASK

1. Start with FROM ubuntu24.04 and then make sure curl and dnsutils are installed in the container image.
2. Start and execute into the container image, then try using the curl and nslookup tools.

2. static-web-app

Static nginx-based web-app which hosts static HTML files.

TASK

1. Create a static http web-app that hosts our static replacement index.html file.
2. You can use nginx, python -m http.server or any other way to host the static html/index.html file via HTTP on an exposed port.

3. micro-go-app

Simple scratch-based go app that just outputs the contents of a .txt file

TASK

1. This task is purely educational. Inspect the Dockerfile and learn about scratch
2. Build the container image and check its disk-size! docker images | grep <image-tag>

java-hello-world

Simple hello-world app in Java

TASK

1. Follow Ole's guide on containerizing a Java app

dotnet-hello-world

Simple hello-world app in .NET 10

Create a Dockerfile for the app and test it!

TASK

1. Follow Microsoft's guide on containerizing dotnet apps
2. See https://learn.microsoft.com/en-us/dotnet/core/docker/build-container?tabs=windows&pivots=dotnet-10-0

Best practices

• Minimize layers by combining related commands.
• Split Dockerfile into build and runtime stages! (massively reduces image size)
• Use .dockerignore to reduce the build-context and image size.
• Pin versions! Use FROM alpine:3.19.0 rather than just alpine or alpine:latest.
  • Use of :stable tags might be a good idea if available.
• Add metadata to your container images!

  LABEL org.opencontainers.image.source="https://github.com/org/repo"
  LABEL org.opencontainers.image.version="1.0.0"
  LABEL org.opencontainers.image.description="My custom base image"
  

Bonus assignments

1. Use docker compose up -d to build and launch all our containers (in the same virtual network).
2. Try executing into on of the running containers (docker compose exec -it <service-name> /bin/bash).
3. Try to fetch our HTML website from static-web-app via the ubuntu-debugger container.
4. Try fetching logs from our static-web-app via cmd docker compose logs -f <service-name>, can you see the fetch?
5. Try reducing some of the container image sizes! Check with docker images.