Written by Vignesh Ragupathy
on 
[ kubernetes  linux  opensource  ]

Creating persistent local-storage volume in Kubernetes

PersistentVolume and PersistentVolumeClaim in kubernetes provides a way to allocate storage for the pods. Kubernetes PV supports different types of storage. Now here in the below post we are going to use storage-class local-storage and watch the behaviour for different reclaimpolicy.

Setup

I am using the Virtualbox(running in Ubuntu 18.04 physical machine) for this entire setup . The physical machine is Dell inspiron laptop with 12GB RAM , Intel® Core™ i7-6500U CPU @ 2.50GHz × 4 and 512GB SSD hardisk.

Step 1: Create a directory in one for the node and add a file
root@kubernetes2:~# mkdir /pvdir
root@kubernetes2:~# echo "Hello world!" > /pvdir/index.html 
root@kubernetes2:~# cat /pvdir/index.html 
Hello world!
Step 2: Get the label of the node

We need to get the label of the node where the directory is created.This we need to configure  in the nodeAffinity specs in order to properly stick the pod to respective node where the local volume is present.

vikki@kubernetes1:~$ kubectl get nodes --show-labels
NAME STATUS ROLES AGE VERSION LABELS
kubernetes1 Ready master 19d v1.16.2 beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=kubernetes1,kubernetes.io/os=linux,node-role.kubernetes.io/master=
kubernetes2 Ready <none> 19d v1.16.2 beta.kubernetes.io/arch=amd64,beta.kubernetes.io/os=linux,kubernetes.io/arch=amd64,kubernetes.io/hostname=kubernetes2,kubernetes.io/os=linux
Step 3: Create a persistent volume(PV)

Create a PV and map the local storage director and configure the label in the node selector

vikki@kubernetes1:~$ vim pv.yaml
vikki@kubernetes1:~$ kubectl create -f pv.yaml 
persistentvolume/vikki-pv-volume created
Step 4: Verify the PV status

Verify the PV status. It is currently configured with access type RWO and reclaim policy as Delete

vikki@kubernetes1:~$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
vikki-pv-volume 1Gi RWO Delete Available local-storage 14s
Step 5: Create a persistent volume claim(PVC)

Create a PVC and map the above created PV

vikki@kubernetes1:~$ vim pv_claim.yaml
vikki@kubernetes1:~$ kubectl create -f pv_claim.yaml 
persistentvolumeclaim/vikki-pv-volume-claim created
Step 6: Verify the PVC status

Verify the PVC and PV status. Now we can see the status changes from Available to Bound.

vikki@kubernetes1:~$ kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
vikki-pv-volume-claim Bound vikki-pv-volume 1Gi RWO local-storage 8s
vikki@kubernetes1:~$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
vikki-pv-volume 1Gi RWO Delete Bound default/vikki-pv-volume-claim local-storage 3m59s
Step 7: Create a pod and map the PVC

Create a pod and map the volumes as below

vikki@kubernetes1:~$ kubectl run --image=nginx nginx-pod --generator=run-pod/v1 --dry-run -o yaml > pod.yaml
vikki@kubernetes1:~$ vim pod.yaml
vikki@kubernetes1:~$ kubectl create -f pod.yaml 
pod/nginx-pod created
Step 8: Verify the pod status and volume inside

Verify the status of the new pod and check the volume is mounted inside the container

vikki@kubernetes1:~$ kubectl get pods
NAME READY STATUS RESTARTS AGE
fluentd-elasticsearch-bwhfx 0/1 ImagePullBackOff 0 4h3m
fluentd-elasticsearch-pvlpv 0/1 ImagePullBackOff 0 4h3m
nginx-85ff79dd56-zqllr 1/1 Running 1 5h51m
nginx-pod 1/1 Running 0 10s
root@kubernetes2:~# docker ps -a |grep nginx-pod
e142048a048f nginx "nginx -g 'daemon of…" 20 seconds ago Up 20 seconds k8s_nginx-pod_nginx-pod_default_b6b900bb-b214-4b96-bc90-18b2358ee225_0
df59f401a38a k8s.gcr.io/pause:3.1 "/pause" 26 seconds ago Up 25 seconds k8s_POD_nginx-pod_default_b6b900bb-b214-4b96-bc90-18b2358ee225_0
root@kubernetes2:~# docker exec -it k8s_nginx-pod_nginx-pod_default_b6b900bb-b214-4b96-bc90-18b2358ee225_0 cat /usr/share/nginx/html/index.html
Hello world!

Now we can see the directory from the PV is mounted in the pod and the files created are present

Verify reclaim policy(Below steps are Optional)

Step 9: Delete PVC and verify PV

Now delete the pod and PVC and verify the status of PV

vikki@kubernetes1:~$ kubectl delete pod nginx-pod
pod "nginx-pod" deleted
vikki@kubernetes1:~$ kubectl delete pvc vikki-pv-volume-claim 
persistentvolumeclaim "vikki-pv-volume-claim" deleted
vikki@kubernetes1:~$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
vikki-pv-volume 1Gi RWO Delete Failed default/vikki-pv-volume-claim local-storage 5m30s

We can see the staus of PV is automaticall changed to Failed. This is due the the reclaim policy Delete

Step 10: (Optional ) Try recreate PVC

We can optionally try recreating the PVC volume and verify the status

vikki@kubernetes1:~$ kubectl create -f pv_claim.yaml 
persistentvolumeclaim/vikki-pv-volume-claim created
vikki@kubernetes1:~$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
vikki-pv-volume 1Gi RWO Delete Failed default/vikki-pv-volume-claim local-storage 5m57s
vikki@kubernetes1:~$ kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
vikki-pv-volume-claim Pending local-storage 2m10s

We can see the status of PV is still Failed and the PVC always in Pending and never creates

Step 11: Delete and create PV with reclaim policy as retain

Now lets clean up all PV and PVC and recreate PV with reclaim policy set as “Retain”

vikki@kubernetes1:~$ kubectl delete pvc vikki-pv-volume-claim 
persistentvolumeclaim "vikki-pv-volume-claim" deleted

vikki@kubernetes1:~$ kubectl delete pv vikki-pv-volume 
persistentvolume "vikki-pv-volume" deleted
vikki@kubernetes1:~$ vim pv.yaml
persistentVolumeReclaimPolicy: Retain
vikki@kubernetes1:~$ kubectl create -f pv.yaml 
persistentvolume/vikki-pv-volume created
vikki@kubernetes1:~$ kubectl create -f pv_claim.yaml 
persistentvolumeclaim/vikki-pv-volume-claim created
vikki@kubernetes1:~$ kubectl get pvc,pv
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
persistentvolumeclaim/vikki-pv-volume-claim Bound vikki-pv-volume 1Gi RWO local-storage 99s

NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
persistentvolume/vikki-pv-volume 1Gi RWO Retain Bound default/vikki-pv-volume-claim local-storage 118s
Step 12: Delete the PVC and verify the status of PV

Now lets delete the PVC and verify the status of the PV

vikki@kubernetes1:~$ kubectl delete pvc vikki-pv-volume-claim 
persistentvolumeclaim "vikki-pv-volume-claim" deleted
vikki@kubernetes1:~$ kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
vikki-pv-volume 1Gi RWO Retain Released default/vikki-pv-volume-claim local-storage 2m11s

Now we can see the status of PV changes to “Released” instead of “Failed” due to the reclaim policy “Retain”

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