We can attach persistent volumes to Pods, these volumes remain unchanged even when there is a Pod failure, Google compute engine standard persistent disk is an example of persistent volume on the Cloud.

 

Let’s create a blank disk in the same zone as the Kubernetes cluster

Screenshot 2019-03-28 at 7.47.33 PM.png

To view the list of compute engine disks

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ gcloud compute disks list
NAME                                               ZONE SIZE_GB TYPE STATUS
disk-1                                             us-east1-b 10 pd-standard  READY
gke-standard-cluster-1-default-pool-a97a9634-019h  us-central1-a 100 pd-standard READY
gke-standard-cluster-1-default-pool-a97a9634-glnz  us-central1-a 100 pd-standard READY
gke-standard-cluster-1-default-pool-a97a9634-rxrw  us-central1-a 100 pd-standard READY
networkandcode@cloudshell:~ (kubernetes-cka-224606)$

 

We need to refer the name of this disk, in our Pod definition

 

Let’s view the Pod definition

 

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ cat podWithPersistentVolume.yaml
---
apiVersion: v1
kind: Pod
metadata:
  name: apache-pod
spec:
  containers:
  - name: apache-container
    image: httpd
    volumeMounts:
    - name: apache-volume
      mountPath: /tmp/apache
  volumes:
  - name: apache-volume
    gcePersistentDisk:
      pdName: disk-1
...

 

Let’s create the Pod

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl create -f podWithPersistentVolume.yaml
pod "apache-pod" created

 

The Pod is successfully running

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl get pods
NAME         READY STATUS    RESTARTS AGE
apache-pod   1/1 Running   0 20s

 

Let’s view more details about the Pod

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl describe po/apache-pod

…TRUNCATED

Volumes:
  apache-volume:
    Type:       GCEPersistentDisk (a Persistent Disk resource in Google Compute Engine)
    PDName:     disk-1

…TRUNCATED

Events:
  Type    Reason                Age From                                          Message
  ----    ------                ---- ----                                          -------
  Normal  Scheduled               50s default-scheduler                                          Successfully assigned default/apache-pod to gke-standard-cluster-1-defaul
t-pool-a97a9634-glnz
  Normal  SuccessfulAttachVolume  42s attachdetach-controller                                     AttachVolume.Attach succeeded for volume "apache-volume"
  Normal  Pulling                40s kubelet, gke-standard-cluster-1-default-pool-a97a9634-glnz  pulling image "httpd"
  Normal  Pulled                40s kubelet, gke-standard-cluster-1-default-pool-a97a9634-glnz  Successfully pulled image "httpd"
  Normal  Created                40s kubelet, gke-standard-cluster-1-default-pool-a97a9634-glnz  Created container
  Normal  Started                40s kubelet, gke-standard-cluster-1-default-pool-a97a9634-glnz  Started container

 

Let’s login to the Pod and launch bash

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl exec -it apache-pod -- /bin/bash
root@apache-pod:/usr/local/apache2#

To change the directory to the volume mount path, as specified in the Pod definition
root@apache-pod:/usr/local/apache2# cd /tmp/apache

 

Let’s create a text file and add some text to it

root@apache-pod:/tmp/apache# echo "Sample Text" > test.txt
root@apache-pod:/tmp/apache# ls
lost+found  test.txt
root@apache-pod:/tmp/apache# cat test.txt
Sample Text

 

To exit out of the Pod

root@apache-pod:/tmp/apache# exit
exit

 

To delete the Pod
networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl delete pod apache-pod
pod "apache-pod" deleted

 

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl get pods
No resources found.

 

To create the Pod again

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl apply -f podWithPersistentVolume.yaml
pod "apache-pod" created

 

To getinto the bash prompt of the Pod

networkandcode@cloudshell:~ (kubernetes-cka-224606)$ kubectl exec -it apache-pod -- /bin/bash

 

To check the contents of the volume mount path

root@apache-pod:/usr/local/apache2# ls /tmp/apache/
lost+found  test.txt

 

The file is still there as the volume is persistent
root@apache-pod:/usr/local/apache2# cat /tmp/apache/test.txt
Sample Text

 

--end-of-post--