K8s-PersistantVolume.md

LAB: K8s Persistent Volumes and Persistent Volume Claims

This scenario shows how K8s PVC and PV work on minikube

Steps

• On Minikube, we do not have to reach NFS Server. So we simulate NFS Server with Docker Container.

docker volume create nfsvol
docker network create --driver=bridge --subnet=10.255.255.0/24 --ip-range=10.255.255.0/24 --gateway=10.255.255.10 nfsnet
docker run -dit --privileged --restart unless-stopped -e SHARED_DIRECTORY=/data -v nfsvol:/data --network nfsnet -p 2049:2049 --name nfssrv ozgurozturknet/nfs:latest

• Now our simulated server enabled.
• Copy and save (below) as file on your PC (pv.yaml).

apiVersion: v1                               
kind: PersistentVolume
metadata:
   name: mysqlpv
   labels:
     app: mysql                                # labelled PV with "mysql"
spec:
  capacity:
    storage: 5Gi                               # 5Gibibyte = power of 2; 5GB= power of 10
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain      
  nfs:
    path: /                                    # binds the path on the NFS Server
    server: 10.255.255.10                      # IP of NFS Server

• Create PV object on our cluster:

• Copy and save (below) as file on your PC (pvc.yaml).

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysqlclaim
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem          
  resources:
    requests:
      storage: 5Gi
  storageClassName: ""
  selector:
    matchLabels:
      app: mysql                     # chose/select "mysql" PV that is defined above.

• Create PVC object on our cluster. After creation, PVC's status shows to bind to PV ("Bound"):

• Copy and save (below) as file on your PC (deploy.yaml).

apiVersion: v1                                     # Create Secret object for password
kind: Secret
metadata:
  name: mysqlsecret
type: Opaque
stringData:
  password: P@ssw0rd!
---
apiVersion: apps/v1
kind: Deployment                                  # Deployment
metadata:
  name: mysqldeployment
  labels:
    app: mysql
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mysql                                   # select deployment container (template > metadata > labels)
  strategy:
    type: Recreate
  template:
    metadata:
      labels:  
        app: mysql
    spec:
      containers:
        - name: mysql
          image: mysql
          ports:
            - containerPort: 3306
          volumeMounts:                             # VolumeMounts on path and volume name
            - mountPath: "/var/lib/mysql"
              name: mysqlvolume                     # which volume to select (volumes > name)
          env:
            - name: MYSQL_ROOT_PASSWORD
              valueFrom:                            # get mysql password from secrets
                secretKeyRef:
                  name: mysqlsecret
                  key: password
      volumes:
        - name: mysqlvolume                         # name of Volume
          persistentVolumeClaim:
            claimName: mysqlclaim                   # chose/select "mysqlclaim" PVC that is defined above.

• Run deployment on our cluster:

• Watching deployment status:

• See the details of pod (mounts and volumes):

• Enter into the pod and see the path that the volume is mounted ("kubectl exec -it -- bash"):

• If the new node is added into the cluster and this running pod is stopped running on the main minikube node, the pod will start on the another node.
• With this scenario, we can see the followings:
  • Deployment always run pod on the cluster.
  • The pod which is created on the new node still connects the persistent volume (there is not any loss for volume)
  • How assigning taint on the node (key:=value:NoExecute, if NoExecute is not tolerated by pod, pod is deleted on the node)

• New pod is created on the new node (2nd node)

• Second pod also is connected to the same volume again.

• Enter into the 2nd pod and see the path that the volume is mounted ("kubectl exec -it -- bash"). When you see the files at the same path on the 2nd pod, volume files are same:

• Delete minikube, docker container, volume, network:

References

• https://github.com/aytitech/k8sfundamentals/tree/main/pvpvc