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Playing With Gce Persistent Disk in K8s

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playing with gce persistent disk in k8s

Find out the region of your cluster

gcloud container clusters list |sed -r 's/ +/ /g'|cut -f2 -d ' '

LOCATION
europe-west1-d

Then, create the disk in this region.

gcloud compute disks create --size=10GB --zone=europe-west1-d slo-test-disk

NAME           ZONE            SIZE_GB  TYPE         STATUS
slo-test-disk  europe-west1-d  10       pd-standard  READY

gke does not want to hear about disks under 10GB…

Then, create the associated PersistentVolume,

apiVersion: "v1"
kind: "PersistentVolume"
metadata:
  name: "slo-pv"
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - "ReadWriteOnce"
  gcePersistentDisk:
    fsType: "ext4"
    pdName: "slo-test-disk"

Then, add it to k8s

kta ~/test/k8s/pv.yaml

persistentvolume/slo-pv created

See if the PV is correctly associated to the gce persistent disk

ktl describe pv slo-pv

Name:              slo-pv
Labels:            failure-domain.beta.kubernetes.io/region=europe-west1
                   failure-domain.beta.kubernetes.io/zone=europe-west1-d
Annotations:       pv.kubernetes.io/bound-by-controller: yes
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:
Status:            Bound
Claim:             default/slo-pvc
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          10Gi
Node Affinity:
  Required Terms:
    Term 0:        failure-domain.beta.kubernetes.io/zone in [europe-west1-d]
                   failure-domain.beta.kubernetes.io/region in [europe-west1]
Message:
Source:
    Type:       GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
    PDName:     slo-test-disk
    FSType:     ext4
    Partition:  0
    ReadOnly:   false
Events:         <none>

Great,

Create the PVC.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: slo-pvc
spec:
  storageClassName: "" # Empty string must be explicitly set otherwise default StorageClass will be set
  volumeName: slo-pv
  resources:
    requests:
      storage: 100Mi
  accessModes:
    - ReadWriteOnce

kta ~/test/k8s/pvc.yaml

persistentvolumeclaim/slo-pvc created

Is it correctly bound to the PV?

ktl describe pvc slo-pvc

Name:          slo-pvc
Namespace:     default
StorageClass:
Status:        Bound
Volume:        slo-pv
Labels:        <none>
Annotations:   pv.kubernetes.io/bind-completed: yes
Finalizers:    [kubernetes.io/pvc-protection]
Capacity:      10Gi
Access Modes:  RWO
VolumeMode:    Filesystem
Mounted By:    slo-pod
Events:        <none>

Great,

Now, let’s try to write something into this volume, with a simple pod.

apiVersion: v1
kind: Pod
metadata:
  name: slo-writer
spec:
  containers:
    - name: slo
      image: busybox
      command: ["sh"]
      args: ["-c", "echo test > /volume/test && sleep 3600"]
      volumeMounts:
      - mountPath: "/volume"
        name: slo-volume
  volumes:
    - name: slo-volume
      persistentVolumeClaim:
        claimName: slo-pvc

kta ~/test/k8s/writer.yaml

pod/slo-pod created

Check that the pod is correctly bound

ktl describe pod slo-pod |gi slo-pv

    ClaimName:  slo-pvc
  Normal   SuccessfulAttachVolume  52s                attachdetach-controller  AttachVolume.Attach succeeded for volume "slo-pv"
Name:              slo-pv
Labels:            failure-domain.beta.kubernetes.io/region=europe-west1
                   failure-domain.beta.kubernetes.io/zone=europe-west1-d
Annotations:       pv.kubernetes.io/bound-by-controller: yes
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:
Status:            Bound
Claim:             default/slo-pvc
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          10Gi
Node Affinity:
  Required Terms:
    Term 0:        failure-domain.beta.kubernetes.io/zone in [europe-west1-d]
                   failure-domain.beta.kubernetes.io/region in [europe-west1]
Message:
Source:
    Type:       GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
    PDName:     slo-test-disk
    FSType:     ext4
    Partition:  0
    ReadOnly:   false
Events:         <none>

Is it running?

ktl get pod slo-pod

NAME      READY   STATUS    RESTARTS   AGE
slo-pod   1/1     Running   0          68s

Nice, let’s take a look at the content of the volume.

ktl exec slo-pod ls /volume

lost+found
test

Ok, now let’s take a look at the gce disk content, just to make sure the content is there.

Those are in this

Hmm, looks like I cannot see the content of gce persistent disk from here.

At least, let’s start another pod to read the content and see if we find out the wrote file.

apiVersion: v1
kind: Pod
metadata:
  name: slo-reader
spec:
  containers:
    - name: slo
      image: busybox
      command: ["sh"]
      args: ["-c", "ls /volume/ && sleep 3600"]
      volumeMounts:
      - mountPath: "/volume"
        name: slo-volume
  volumes:
    - name: slo-volume
      persistentVolumeClaim:
        claimName: slo-pvc

kta ~/test/k8s/reader.yaml

pod/slo-reader created

Then, look at its output

ktl logs slo-reader

lost+found
test

Great, the content is there.

No, let’s close the pods to see if the content actually persists.

ktd ~/test/k8s/writer.yaml
ktd ~/test/k8s/reader.yaml

pod "slo-writer" deleted
pod "slo-reader" deleted

Now, let’s spawn the reader another time

kta ~/test/k8s/reader.yaml

pod/slo-reader created

Then, look at its output

ktl logs slo-reader

lost+found
test

Ok, just like we expected.

Just to be sure, let’s write another thing before concluding.

apiVersion: v1
kind: Pod
metadata:
  name: slo-writer2
spec:
  containers:
    - name: slo
      image: busybox
      command: ["sh"]
      args: ["-c", "echo test > /volume/test2 && sleep 3600"]
      volumeMounts:
      - mountPath: "/volume"
        name: slo-volume
  volumes:
    - name: slo-volume
      persistentVolumeClaim:
        claimName: slo-pvc

kta ~/test/k8s/writer2.yaml

pod/slo-writer2 created

kta ~/test/k8s/reader.yaml

pod/slo-reader created

ktl logs slo-reader

lost+found
test
test2

Ok, now I feel like this is working,

Lets clean a bit

ktd ~/test/k8s/ -R

gcloud compute disks delete --zone=europe-west1-d slo-test-disk