GKE how to use existing compute engine disk as persistent volumes? - google-cloud-platform

Question

I might have to rebuild the GKE cluster but the compute engine disks won't be delete and needs to be re-used as persistent volumes for the pods. I haven't found a documentation showing how to link the existing GCP compute engine disk as persistent volumes for the pods.
Is it possible to use the existing GCP compute engine disks with GKE storage class and Persistent volumes?

Answer 1

Yes, it's possible to reuse Persistent Disk as Persistent Volume for another clusters, however there is one limitation:
The persistent disk must be in the same zone as the cluster nodes.
If PD will be in a different zone, the cluster will not find this disk.
In Documentation Using preexisting persistent disks as PersistentVolumes you can find information and examples how to reuse persistent disks.
If you didn't create Persistent Disk yet, you can create it based on Creating and attaching a disk documentation. For this tests, I've used below disk:
gcloud compute disks create pd-name \
--size 10G \
--type pd-standard \
--zone europe-west3-b
If you will create PD with less than 200G you will get below Warning, everything depends on your needs. In zone europe-west3-b, pd-standard type can have storage between 10GB - 65536GB.
You have selected a disk size of under [200GB]. This may result in poor I/O performance. For more information, see: https://developers.google.com/com
pute/docs/disks#performance.
Keep in mind that you might get different types of Persistent Disk on different zones. For more details you can check Disk Types documentation or run $ gcloud compute disk-types list.
Once you have Persistent Disk you can create PersistentVolume and PersistentVolumeClaim.
apiVersion: v1
kind: PersistentVolume
metadata:
name: pv
spec:
storageClassName: "test"
capacity:
storage: 10G
accessModes:
- ReadWriteOnce
claimRef:
namespace: default
name: pv-claim
gcePersistentDisk:
pdName: pd-name
fsType: ext4
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: pv-claim
spec:
storageClassName: "test"
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 10G
---
kind: Pod
apiVersion: v1
metadata:
name: task-pv-pod
spec:
volumes:
- name: task-pv-storage
persistentVolumeClaim:
claimName: pv-claim
containers:
- name: task-pv-container
image: nginx
ports:
- containerPort: 80
name: "http-server"
volumeMounts:
- mountPath: "/usr/data"
name: task-pv-storage
Tests
$ kubectl get pv,pvc,pod
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
persistentvolume/pv 10G RWO Retain Bound default/pv-claim test 22s
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/pv-claim Bound pv 10G RWO test 22s
NAME READY STATUS RESTARTS AGE
pod/task-pv-pod 1/1 Running 0 21s
Write some information to disk
$ kubectl exec -ti task-pv-pod -- bin/bash
root#task-pv-pod:/# cd /usr/share/nginx/html
root#task-pv-pod:/usr/share/nginx/html# echo "This is test message from Nginx pod" >> message.txt
Now I removed all previous resources: pv, pvc and pod.
$ kubectl get pv,pvc,pod
No resources found
Now If I would recreate pv, pvc with small changes in pod, for example busybox.
containers:
- name: busybox
image: busybox
command: ["/bin/sh"]
args: ["-c", "while true; do echo hello; sleep 10;done"]
volumeMounts:
- mountPath: "/usr/data"
name: task-pv-storage
It will be rebound
$ kubectl get pv,pvc,po
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
persistentvolume/pv 10G RWO Retain Bound default/pv-claim 43m
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/pv-claim Bound pv 10G RWO 43m
NAME READY STATUS RESTARTS AGE
pod/busybox 1/1 Running 0 3m43s
And in the busybox pod I will be able to find Message.txt.
$ kubectl exec -ti busybox -- bin/sh
/ # cd usr
/ # cd usr/data
/usr/data # ls
lost+found message.txt
/usr/data # cat message.txt
This is test message from Nginx pod
As additional information, you won't be able to use it in 2 clusters in the same time, if you would try you will get error:
AttachVolume.Attach failed for volume "pv" : googleapi: Error 400: RESOURCE_IN_USE_B
Y_ANOTHER_RESOURCE - The disk resource 'projects/<myproject>/zones/europe-west3-b/disks/pd-name' is already being used by 'projects/<myproject>/zones/europe-west3-b/instances/gke-cluster-3-default-pool-bb545f05-t5hc'