Level 1 exam — Docker · GUIDINEE.COM

Exam — fresh questions

12 questions to validate Containers: images, volumes, networks — tags, running, persistence, networks, debugging.
Answer everything, then click Check: your score and explanations will appear.

1.1 · Recall

1. What does the tag mean in 'postgres:16.4'?

The pinned version (major 16, minor 4) of the image The database password The container's network name A comment with no effect on the image

The tag designates the variant: 16 pins the major, 16.4 the minor — reproducible, unlike latest.

1.1 · Application

2. Idir is preparing the production database. Which image should he keep?

Official postgres:16.4, pinned, noted in versions.txt postgres:latest to always have the newest The first image with 'postgres' in its name An image not updated for two years, but lighter

Official, up to date, pinned and noted tag: the only acceptable combination in production.

1.1 · Application

3. Why do ten images based on the same Debian download the base only once?

Because latest avoids duplicates Because Docker compresses everything into a single file Because layers are shared and cached Because images are stored on Docker Hub

Read-only layers are shared: only missing layers are downloaded.

1.2 · Recall

4. In '-p 8080:80', what do 8080 and 80 mean?

8080 = container, 80 = host Two ports internal to the container 8080 = host port, 80 = container port An identifier and a password

Left = host, right = container: http://localhost:8080 reaches port 80 of the container.

1.2 · Application

5. Idir launches a long-lived Nginx server. Which command?

docker run -d --name web nginx (no tag) docker exec -it web sh docker run -it nginx:1.27 (attached terminal) docker run -d --name web -p 8080:80 nginx:1.27

Service = -d (background) + --name (manageable) + -p (reachable) + pinned tag; -it would block the terminal.

1.2 · Arbitration

6. The password passed with -e must change. What is the right call?

Delete and relaunch with the new value (variables frozen at creation) Change the image tag Restart the container, the variable will follow Edit the variable in the running container

Variables with -e are frozen at creation: delete and relaunch — or version via Compose (level 3).

1.3 · Application

7. Idir wants his database to survive rm of the container. What should he do?

Copy the data into the image Launch two identical containers Using stop instead of rm is enough Mount a named volume at the documented path (-v pgdata:/var/lib/postgresql/data)

Only a mount outside the container survives rm; stop keeps everything but is not persistence.

1.3 · Arbitration

8. Should you run 'docker volume prune' on a shared machine without checking?

Yes, volumes can be restored from the trash No: deletion is final — list and identify before any cleanup No, because prune never deletes anything Yes, it only touches stopped containers

prune permanently deletes orphan volumes: list (ls), identify, then clean.

1.4 · Recall

9. What do you gain with a dedicated network (network create) versus the default bridge?

Containers faster to download Resolving containers by their name Lighter images Automatic data persistence

A dedicated network enables DNS by name: no more changing IPs of the default bridge.

1.4 · Application

10. On monapp, how does the web reach the database named 'bdd'?

By merging both containers By its IP written on a sticky note By publishing the database with -p to the outside By its name: bdd:5432, database unpublished

The name stays valid after every relaunch; the database stays internal, only the frontend is published.

1.5 · Application

11. Idir's web is in Exited (1). First reflex?

Recreate immediately identically Read the logs (then inspect) to name the cause Switch images at random Edit files in the stopped container

State guides, logs accuse, inspection confirms: fix the cause, not the symptom.

1.5 · Arbitration

12. 'docker exec -it web sh' answers 'container not running'. What is the right call?

Publish an extra port to unblock exec Force another shell, exec always ends up getting in exec requires a running container: read logs + inspect, start or inspect via run --rm Delete the image and reinstall everything

exec = running; stopped = logs + inspect first, then start or throwaway inspection of the image.

What's next?

Score ≥ 80%: move to V3 Level 2 (Dockerfile, build, configuration — building your own images).
Score between 50% and 80%: review the missed sections (pinned tags in 1.1, host:container order in 1.2, rm + relaunch test in 1.3, dedicated network in 1.4, ps → logs → inspect method in 1.5), reread the explanations above, then retake the test.
Score < 50%: restart the level by running each template (versions.txt in 1.1, launch line in 1.2, persistent database in 1.3, two-service app in 1.4, autopsy checklist in 1.5) with Idir — and only ship what survives rm and answers ping.