DOCKER · Storage · 8 min

Keep data after a container exits

Write a named volume, then read it from a new container.

Not completed

Your task

Create the named practice volume, write persistent-note into /data/message.txt, then read it from a different temporary container into volume.txt.

What you’re aiming for

volume.txt contains persistent-note.
The named volume remains after both temporary containers exit.

1. Prepare your practice folder

Use a running Docker engine in Linux container mode. The setup commands below use a Bash-compatible shell: Git Bash on Windows, or Bash on Linux/macOS.

Create a new, empty folder for this exercise. If that name already exists, choose another new name. Continue only after you’re inside the new folder.

NEW PRACTICE FOLDER

mkdir opsrung-docker-persist-volume-data && cd opsrung-docker-persist-volume-data

Run these setup commands in that folder:

SETUP — RUN ONCE

cat > Dockerfile <<'DOCKERFILE'
FROM alpine:3.22
RUN mkdir /data && chown 65534:65534 /data
USER 65534:65534
CMD ["sleep","3600"]
DOCKERFILE
docker build -t opsrung-persist-volume-data:practice .

Docker may download the official Alpine image and, for the web task, its HTTP package. If an example container name already exists, use a different name consistently. If port 8088 is occupied, choose another free local port.

2. Try the task

Work toward the goal above. Start by inspecting the files or resources, then use a hint if you need one.

Hint 1

A named volume is separate from a container’s writable layer.

Hint 2

Mount the same volume at /data in both runs.

Hint 3

The supplied image gives its unprivileged user ownership of /data.

3. Review your result

Use these commands to look at your result and compare it with the goals. The website does not run or verify them.

REVIEW IN YOUR TERMINAL

cat volume.txt
docker volume inspect opsrung-persist-volume-data-data

What you should see

volume.txt contains persistent-note.
The named volume remains after both temporary containers exit.

If your result differs: Compare the actual output with each goal. Keep your work inside this exercise’s folder and use only its named resources.

Compare with one possible solution

ONE POSSIBLE SOLUTION

docker volume create opsrung-persist-volume-data-data
docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges --mount type=volume,source=opsrung-persist-volume-data-data,target=/data opsrung-persist-volume-data:practice sh -c "printf 'persistent-note\n' > /data/message.txt"
docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges --mount type=volume,source=opsrung-persist-volume-data-data,target=/data opsrung-persist-volume-data:practice cat /data/message.txt > volume.txt

Other approaches are fine if you reach the same goal. Opening this solution does not mark the exercise complete.

Clean up this exercise

Only remove the example resources you created. Volume cleanup deletes that exercise’s saved sample data. Keep anything you need.

OPTIONAL CLEANUP

docker volume rm opsrung-persist-volume-data-data
docker image rm opsrung-persist-volume-data:practice

Finished this exercise?

You decide when you’re done. Your choice is saved in this browser, and you can change it later.