are VOLUME in Dockerfile persistent in kubernetes

Question

Some Dockerfile have a VOLUME command.

What happens when such containers are deployed in Kubernetes, but no kubernetes volume are provided: no persistent volume (PV), nor

Answer 1

(answer based on what I observed with Rancher 2.4, kubernetes 1.17 using Docker)

Short answer:

a Docker volume is created in /var/lib/docker/volumes/... and removed when the pods is stopped or redeployed.

Long answer:

Kubernetes doesn't seems to have any knowledge of the volume the containers / in the Dockerfile. No Kubernetes objects seems to be created.

When Kubernetes tell Docker daemon to start a container, Docker creates a volume (like docker volume create) and attach the created volume (unless kubernete's provides a volume to mount).

Where are the file stored ?

The file is a regular Docker volume (see docker volume below)

Is the volume persistent ?

No, the docker volume is removed when the pod is removed (like if you ran docker rm $mycontainer --volumes)

---

    docker inspect 6ce5f52186d4 | grep '"Driver": "local"' -A5 -B5

            {
                "Type": "volume",
                "Name": "679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39",
                "Source": "/var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/_data",
                "Destination": "/var/lib/postgresql/data",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }

 $ docker volume ls
DRIVER              VOLUME NAME
local               679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39

 $ du -hs /var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/
51.4M   /var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/