9. Volumes and Bind Mounts

Storage Choices

Storage	Typical use
Container writable layer	Disposable runtime files
Named volume	Application data managed independently of a container
Bind mount	Files at a specific path on the daemon host
tmpfs mount	Temporary memory-backed files on supported hosts

Removing a container removes its writable layer. A named volume survives removal of the container that used it.

Verify Persistence

docker volume create docker-course-data
docker run --rm --mount type=volume,src=docker-course-data,dst=/data busybox:1.37 sh -c 'echo persistent > /data/message.txt'
docker run --rm --mount type=volume,src=docker-course-data,dst=/data,readonly busybox:1.37 cat /data/message.txt

Expected output: persistent. The writer container was removed, but a different container can still read the file.

Common Mistakes

Writing important data only inside the container layer.
Mounting a volume at the wrong application path.
Forgetting that mounting over an image directory hides the files beneath that mount.
Treating persistence as a backup strategy.

Cleanup

After finishing the exercise, delete its practice data:

docker volume rm docker-course-data

Quick Interview Answer

A volume separates persistent data from container lifetime. A bind mount exposes a chosen host path; a named volume is managed by Docker.

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