Kubernetes Persistent Volume

PVCs are requests for those resources and also act as claim checks to the resource. So a persistent volume (PV) is the "physical" volume on the host machine that stores your persistent data. A persistent volume claim (PVC) is a request for the platform to create a PV for you, and you attach PVs to your pods via a PVC.

The Local Persistent Volumes feature has been promoted to GA in Kubernetes 1.14. A local persistent volume represents a local disk directly-attached to a single Kubernetes Node.

In the Kubernetes system, local disks can be used through HostPath, LocalVolume.

• HostPath: The volume itself does not contain scheduling information. If you want to fix each pod on a node, you need to configure scheduling information, such as nodeSelector, for the pod.
• LocalVolume: The volume itself contains scheduling information, and the pods using this volume will be fixed on a specific node, which can ensure data continuity.
  
  
  

Local Persistent Volumes allow you to access local disk by using the standard PVC object.

Create StorageClass with WaitForFirstConsumer Binding Mode

First, a StorageClass should be created that sets volumeBindingMode: WaitForFirstConsumer to enable volume topology-aware scheduling. This mode instructs Kubernetes to wait to bind a PVC until a Pod using it is scheduled.

storage.yml
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

Prepare volume on the host

# Execute these commands on the worker node where the POD will be located
mkdir -p /data/volumes/pv1
chmode 777 /data/volumes/pv1

Create Local PersistentVolume

Create PersistentVolume with a reference to local-storage StorageClass

PersistentVolume.yml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: test-local-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage
  local:
    path: /data/volumes/pv1
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - master
          - wokernode 

Create a PersistentVolumeClaim

Create PersistentVolumeClaim with a reference to local-storage StorageClass

PersistentVolumeClaim.yml

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: test-pvc
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: local-storage
  resources:
    requests:
      storage: 10Gi

     

The status of test-local-pv is Available because the POD has not yet been created.

Create a POD with local persistent volume

pod.yml
apiVersion: v1
kind: Pod
metadata:
  name: test-local-vol
  labels:
    name: test-local-vol
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
      - name: local-persistent-storage
        mountPath: /usr/share/nginx/html
  volumes:
    - name: local-persistent-storage
      persistentVolumeClaim:
        claimName: test-pvc


and create service manifest for service to access 
svc.yml

kind: kind: Service
apiVersion: v1
metadata:
  name:  Service Name
spec:
  selector:
    name: test-local-vol
  type:  NodePort
  ports:
  - name:  http
    port:  80
    targetPort:  80
    nodePort: 31123

Check the status of PersistentVolume and PersistentVolumeClaim

[root@master pvc]# kubectl apply -f PersistentVolumeClaim.yml -f PersistentVolume.yml -f storage.yml -f pod.yml -f svc.yml
persistentvolumeclaim/test-pvc created
persistentvolume/test-local-pv created
storageclass.storage.k8s.io/local-storage created
pod/test-local-vol created
service/svc created

[root@master ec2-user]# kubectl get pv
NAME            CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM              STORAGECLASS    REASON   AGE
test-local-pv   10Gi       RWO            Retain           Bound    default/test-pvc   local-storage            78m
[root@master ec2-user]# kubectl get pvc
NAME       STATUS   VOLUME          CAPACITY   ACCESS MODES   STORAGECLASS    AGE
test-pvc   Bound    test-local-pv   10Gi       RWO            local-storage   78m
[root@master ec2-user]#

You can see the file on the host’s path.

cd /data/volumes/pv1/     #persistent storage path git clone https://github.com/GudditiNaganjaneyulu/MyResume.gitmv -r MyResume/* .access the application using port NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP        4d20h
svc          NodePort    10.98.114.169   <none>        80:31123/TCP   4m9s  
http://<node ip:31123>Note: Even If your pod dies/deletes the volume claim can be binded again to path with have same previous data .

Summary
The primary benefit of Local Persistent Volumes over remote persistent storage is performance: local disks usually offer higher IOPS and throughput and lower latency compared to remote storage systems. Kubernetes local volumes have following features:
PersistentVolumeClaim will wait for a POD to show up before a local persistent volume is bound
Once a local persistent volume is bound to a claim, it remains bound, even if the requesting POD has died or has been deleted
A new POD can attach to the existing data in a local volume by referencing the same PersistentVolumeClaim
Similar to NFS shares, Kubernetes persistent local volumes allow multiple PODs to have read/write access
Examples of good workloads include software defined storage systems and replicated databases. Other types of applications should continue to use highly available, remotely accessible, durable storage.