Pod access PVC subdirectory that already existed - kubernetes

Question

I have a pod created using a deployment using git-sync image and mount the volume to a PVC
kind: Deployment
metadata:
name: config
namespace: test
spec:
replicas: 1
selector:
matchLabels:
demo: config
template:
metadata:
labels:
demo: config
spec:
containers:
- args:
- '-ssh'
- '-repo=git#domain.com:org/repo.git'
- '-dest=conf'
- '-branch=master'
- '-depth=1'
image: 'k8s.gcr.io/git-sync:v3.1.1'
name: git-sync
securityContext:
runAsUser: 65533
volumeMounts:
- mountPath: /etc/git-secret
name: git-secret
readOnly: true
- mountPath: /config
name: cus-config
securityContext:
fsGroup: 65533
volumes:
- name: git-secret
secret:
defaultMode: 256
secretName: git-creds
- name: cus-config
persistentVolumeClaim:
claimName: cus-config
After the deployment, I checked the pod and got a file path like this.
/tmp/git/conf/subdirA/some.Files
Then I created a second pod from another deployment and want to mount the tmp/git/conf/subdirA on the second pod. This is the example of my second deployment script.
kind: Deployment
metadata:
name: test-mount-config
namespace: test
spec:
replicas: 1
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: 'nginx:1.7.9'
name: nginx
ports:
- containerPort: 80
volumeMounts:
- mountPath: /root/conf
name: config
subPath: tmp/git/conf/subdirA
volumes:
- name: config
persistentVolumeClaim:
claimName: cus-config
This is my PVC
kind: PersistentVolumeClaim
metadata:
annotations:
volume.beta.kubernetes.io/storage-class: conf
name: config
namespace: test
spec:
accessModes:
- ReadWriteMany
resources:
requests:
storage: 10Mi
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: conf
namespace: test
provisioner: spdbyz
reclaimPolicy: Retain
I already read about subpath on PVC, but everytime I checked the folder /root/conf on the second pod, there is nothing inside it.
Any idea on how to mount specific PVC subdirectory on another pod?

Answer 1

Very basic example on how share file content between PODs using PV/PVC
First Create a persistent volume refer below yaml example with hostPath configuration
apiVersion: v1
kind: PersistentVolume
metadata:
name: my-pv-1
labels:
pv: my-pv-1
spec:
capacity:
storage: 1Gi
volumeMode: Filesystem
accessModes:
- ReadWriteMany
persistentVolumeReclaimPolicy: Retain
hostPath:
path: /var/log/mypath
$ kubectl create -f pv.yaml
persistentvolume/my-pv-1 created
Second create a persistent volume claim using below yaml example
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: my-pvc-claim-1
spec:
accessModes:
- ReadWriteMany
resources:
requests:
storage: 1Gi
selector:
matchLabels:
pv: my-pv-1
$ kubectl create -f pvc.yaml
persistentvolumeclaim/my-pvc-claim-1 created
Verify the pv and pvc STATUS is set to BOUND
$ kubectl get persistentvolume
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
my-pv-1 1Gi RWX Retain Bound default/my-pvc-claim-1 62s
$ kubectl get persistentvolumeclaims
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
my-pvc-claim-1 Bound my-pv-1 1Gi RWX 58
Third consume the pvc in required PODs refer below example yaml where the volume is mounted on two pods nginx-1 and nginx-2.
apiVersion: v1
kind: Pod
metadata:
name: nginx-1
spec:
containers:
- image: nginx
name: nginx-1
volumeMounts:
- mountPath: /var/log/mypath
name: test-vol
subPath: TestSubPath
volumes:
- name: test-vol
persistentVolumeClaim:
claimName: my-pvc-claim-1
$ kubectl create -f nginx-1.yaml
pod/nginx-1 created
$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-1 1/1 Running 0 35s 10.244.3.53 k8s-node-3 <none> <none>
Create second POD and consume same PVC
apiVersion: v1
kind: Pod
metadata:
name: nginx-2
spec:
containers:
- image: nginx
name: nginx-2
volumeMounts:
- mountPath: /var/log/mypath
name: test-vol
subPath: TestSubPath
volumes:
- name: test-vol
persistentVolumeClaim:
claimName: my-pvc-claim-1
$ kubectl create -f nginx-2.yaml
pod/nginx-2 created
$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-1 1/1 Running 0 55s 10.244.3.53 k8s-node-3 <none> <none>
nginx-2 1/1 Running 0 35s 10.244.3.54 k8s-node-3 <none> <none>
Test by connecting to container 1 and write to the file on mount-path.
root#nginx-1:/# df -kh
Filesystem Size Used Avail Use% Mounted on
overlay 12G 7.3G 4.4G 63% /
tmpfs 64M 0 64M 0% /dev
tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/vda1 12G 7.3G 4.4G 63% /etc/hosts
shm 64M 0 64M 0% /dev/shm
tmpfs 3.9G 12K 3.9G 1% /run/secrets/kubernetes.io/serviceaccount
tmpfs 3.9G 0 3.9G 0% /proc/acpi
tmpfs 3.9G 0 3.9G 0% /proc/scsi
tmpfs 3.9G 0 3.9G 0% /sys/firmware
root#nginx-1:/# cd /var/log/mypath/
root#nginx-1:/var/log/mypath# date >> date.txt
root#nginx-1:/var/log/mypath# date >> date.txt
root#nginx-1:/var/log/mypath# cat date.txt
Thu Jan 30 10:44:42 UTC 2020
Thu Jan 30 10:44:43 UTC 2020
Now connect tow second POD/container and it should see the file from first as below
$ kubectl exec -it nginx-2 -- /bin/bash
root#nginx-2:/# cat /var/log/mypath/date.txt
Thu Jan 30 10:44:42 UTC 2020
Thu Jan 30 10:44:43 UTC 2020