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A developer on your team suggests this approach:
1. Copy a file with an API key into the Docker image during build.
2. Use it to set up the app.
3. Delete the file in a later step.
Their conclusion: "The file won’t be in the final Docker image, so it’s safe."
You disagree. All layers of a Docker image are kept, so the API key is still there.
Your challenge: Find the API key hidden in the Docker image.
Struggling with Docker issues? This new troubleshooting roadmap can help:
https://www.learnbyfixing.com/roadmaps/docker/
It brings together practical guides and structured skill paths to sharpen your Docker debugging abilities.
New guide released: Namespaces and nsenter
It starts from a simple challenge, but every time you solve it, a new constraint is added, and you have to figure out another way to crack it.
The challenge is this: List all listening TCP ports (IPv4) inside a container.
It includes constraints such as using distroless containers and Docker rootless mode.
After a sudden reorganization, your team has just inherited a legacy Docker image with no docs.
The container starts, but no ports are exposed and the logs are unhelpful.
Right now, the application running inside the container is completely inaccessible.
At first, this feels like a quick fix… until you hit the constraints:
- Distroless image
- Rootless Docker setup
- No sudo access
Can you find and expose the port?
A Docker container can't connect to its own DB, but why?
- DNS resolution?
- Network connectivity?
- Rootless Docker misconfig?
- Or all three at once?
Most container issues aren’t where you think they are.
New hands-on scenario to debug this exact mess:
Most people don't fail at learning Linux troubleshooting… They just don't know what to learn next.
Check out this Linux Troubleshooting Roadmap if you want to:
- Improve your Linux troubleshooting skills
- Stop jumping between random topics
- Follow a clear, practical path
New guide released: Signals in Docker
- Why PID 1 is important inside a container
- docker stop vs docker kill
- How to make containers shut down gracefully
- How to send signals to containers
What is the most effective way to strengthen your troubleshooting skills?
Practice in real scenarios.
We’ve published a GitHub repository with descriptions of all our scenarios, allowing you to explore them and challenge yourself:
https://github.com/learnbyfixing/learnbyfixing
If you find it useful, please give the repo a ⭐!
New scenario released! 🚀
An app was set up locally using Docker Compose... but it doesn't start.
It has 3 services: proxy, app and database.
Can you make it work?
https://www.learnbyfixing.com/scenarios/19/
Happy fixing!
New scenario released! 🚀
You tried to start a containerized app, but it doesn't run.
A colleague says it works on their laptop.
Can you make it run without changing the app's code?
https://www.learnbyfixing.com/scenarios/18/
Happy fixing!
