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Docker for Beginners: Run an App Without Fighting the Host
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Docker for Beginners: Run an App Without Fighting the Host

Final Check: Docker for Beginners

Fifteen scenario questions across the whole course. If you get twelve or more right, you can install Docker, run and debug containers, keep data and start a small stack from one file.

15 min DockerTesting and DebuggingDeployment and Containers Beginner
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1. A coworker says containers are just virtual machines that boot faster. What is the most accurate response?
Containers are isolated processes that share the host's Linux kernel, so they start quickly and need no operating system each. That is right. Each container carries its own kernel. A container is a program that runs without any isolation. Containers need a hypervisor on every machine, like virtual machines.
2. What is the difference between an image and a container?
An image is only the container's name. An image is a read-only package, and a container is a running or stopped copy created from it. A container is stored on Docker Hub, and an image runs on your computer. A container is read-only, and an image is writable.
3. After installing Docker Desktop, you open a PowerShell window that was already open and docker is not recognised. What is the simplest fix?
Run hello-world on Docker Hub's website. Open a new PowerShell window so it picks up the new setup. Disable the WSL 2 engine. Reinstall Windows.
4. What does docker run --name web -d -p 8080:80 nginx:1.30-alpine do?
Builds an image named web from the current folder. Starts a container named web in the background, from the pinned image, with host port 8080 sent to container port 80. Starts nginx in a window and waits until you close it. Opens port 80 on your computer and 8080 in the container.
5. You want to read why a container exited a minute ago. Which command do you use?
docker pull followed by the container name. docker logs followed by the container name. docker exec followed by the container name. docker volume ls
6. What is docker exec -it hello-web sh for?
Copying the shell program to your computer. Stopping hello-web and opening its files in Windows. Opening an interactive shell inside the running container hello-web. Starting a new container named sh.
7. You copied a changed file into a running container with docker cp. When does the change disappear?
After exactly one hour. When the container is removed, because it lived in the container's writable layer. When you close PowerShell. Never. Docker writes it back to the image.
8. In which order does Docker reuse layers when you rebuild an image?
It reuses only the last layer. It never reuses layers. It reuses layers only if you add the cache flag. It reuses each layer until it reaches the first changed instruction, then rebuilds from there on.
9. Which line in a Dockerfile makes a published port reachable from your browser?
EXPOSE 8000 CMD ["python", "app.py"] WORKDIR /app None. Publishing is done when you run the container, with -p.
10. What is the safest way to keep a database's files when its container is removed?
Mount a named volume at the folder where the database stores its data. Publish the data folder as a port. Keep the data in the container and avoid docker rm. Copy the data to the image with docker cp.
11. Containers named db and web are on the default bridge network. web cannot reach http://db. What is the best long-term fix?
Find the IP address of db and hard-code it in web. Publish every port on both containers. Rename db to localhost. Create a user-defined network and attach both containers to it.
12. In a Compose file the web service uses the URL http://quotes/quote.txt. Where does the name quotes come from?
It is a folder on your computer named quotes. It is the name of another service in the same Compose file. It is an address that Docker Hub provides. It is the name of the project.
13. You want to remove one project's containers and network, and nothing else. What do you run?
docker compose down, from the folder with the Compose file. docker system prune -a docker rm -f on every container listed by docker ps docker volume prune
14. A container is listed as Exited (137). What is a reasonable first check?
Whether it was killed for using too much memory, using docker inspect and the OOMKilled field. Whether the image name is spelled correctly. Whether the port is published. Whether the volume has the correct name.
15. A tutorial says docker run nginx. This course writes nginx:1.30-alpine instead. Why?
The tag makes the container run faster than latest does. Docker refuses to run an image without a tag. A pinned tag gives the same version every time, while latest can move to a newer build. The tag is required to publish a port.

About

Fifteen scenario questions across the whole course. If you get twelve or more right, you can install Docker, run and debug containers, keep data and start a small stack from one file.

Duration
15 min
Last update
08/01/2026
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