Docker (Part II)

This exercise aims to learn how to install, run, and understand docker-compose to orchestrate multiple dependent containers.

Exercise Rules

Create an exercise documentation (en|de) while you are working on the tasks.
For every task, write down your initial thoughts, assumptions, and the final outcome in full sentences. Describe the process of solving the task and provide code snippets and screenshots if needed.
If you are not able to solve the task because you are not getting the tool to work, describe how you would solve it theoretically. You should still provide e.g. code snippets or a step by step description from the documentation or tutorial you found.
Provide a hyperlink or other reference for every documentation or tutorial you used to solve a task. Paraphrase and cite correctly, please.
This part of the final submission should be described in at least one, but not more than two A4 pages. Do not submit this exercise alone, but together with the first part. If you did not do the first part, then you should submit what you have, of course.

Use this resource to install docker-compose on your system: https://docs.docker.com/compose/install/. What Problems occur?
Download the following repository to get all needed files: https://github.com/anjakammer/docker-compose_exercise. Analyse the docker-compose file using the docker-compose v3 reference. For every line, write at least one sentence on what it exactly does.
Use the instructions in the README of the repository to run the containers with docker-compose. Explain what happens while starting the containers.
Access the web application in your browser: http://localhost:8081. What does it return exactly? If the application is not running on that address, try to debug this error.
If you manage to run the containers, how can you get the logs using the command line and what can you read out of them?