Docker folders creation and Kubernetes Volume - docker

Question

I have a docker image that creates few folders and extract files into it like below
RUN mkdir -p /home/myapp/myappv4 \
/home/myapp/myappv4/files \
/home/myapp/myappv4/files/logs \
/home/myapp/myappv4/myappentries
WORKDIR /home/myapp
RUN chown -R myapp:myapp /home/myapp
ADD /myapp-v4-files/*.zip /home/myapp/myappv4/files/
ADD /myapp-v4-files/init.txt /home/myapp/myappv4/myappentries/
ADD /myapp-v4-files/pro.json /home/myapp/myappv4/myappentries/
These folders and files needs to be accessed by other containers in a pod in kubernetes. Should i create persistentvolume in kubernetes and have these locations in them and copy the content from this container to this volume? In that way they would not get deleted right?. Since i am new to kubernetes i am not sure on how to achieve this. Transition from docker container to kubernetes deployment seems to be a confusing part for me,any help on this would be appreciated.

Answer 1

If you want to share a set of directories between multiple containers in a single pod, using only EmptyDir volume will suffice. You don't need to use PersistentVolumes (unless you want persistence, meaning you want the data to survive pod restarts).
However note that adding a volume (a kubernetes construct) will overwrite the files already present in your container at the path where you are mounting the volume, kind of what happens with a layered filesystem that docker uses.
For your usecase, I think you can move the file fetching logic from the Dockerfile to a script that the pod will run, that will fix the above mentioned issue.
apiVersion: v1
kind: Pod
metadata:
name: test-pd
spec:
containers:
- image: k8s.gcr.io/test-webserver
name: test-container
volumeMounts:
- mountPath: /cache
name: cache-volume
- image: k8s.gcr.io/test-webserver
name: test-container-2
volumeMounts:
- mountPath: /cache
name: cache-volume
volumes:
- name: cache-volume
emptyDir: {}
Read more about volumes here.