References:
Persistent Volumes
Configure a Pod to Use a PersistentVolume for Storage
Kubernetes 1.14: Local Persistent Volumes GA
Kubernetes API: PersistentVolume
Kubernetes API: PersistentVolumeClaim
Agenda
- PersistentVolume (PV) and PersistentVolumeClaim (PVC) introduction.
- Local Persistent Volume.
- Create local StorageClass, PV, PVC and Pod that uses PVC.
Start a Kubernetes cluster using
minikube start.
PersistentVolume (PV) and PersistentVolumeClaim (PVC)
A PersistentVolume (PV) is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using Storage Classes.
A PersistentVolumeClaim (PVC) is a request for storage by a user. Pods consume node resources and PVCs consume PV resources. Claims can request specific size and access modes (e.g., they can be mounted ReadWriteOnce, ReadOnlyMany or ReadWriteMany, see AccessModes).
Local Persistent Volume
A local persistent volume represents a local disk directly-attached to a single Kubernetes Node.
Local Persistent Volume vs HostPath Volume
With Local Persistent Volumes, the Kubernetes scheduler ensures that a pod using a Local Persistent Volume is always scheduled to the same node. With HostPath volumes, a pod referencing a HostPath volume may be moved by the scheduler to a different node resulting in data loss.
While HostPath volumes may be referenced via a Persistent Volume Claim (PVC) or directly inline in a pod definition, Local Persistent Volumes can only be referenced via a PVC.
Create local directory with index.html on the Node
Open a shell to the single Node in your cluster. For Minikube, you can open a shell to your Node by entering minikube ssh.
Create a /localstore/data directory. This will be used in the PV.
In the /localstore/data directory, create an index.html file.
~/learnk8s> minikube ssh
Last login: Tue May 30 21:10:33 2023 from 192.168.58.1
docker@minikube:~$ sudo mkdir -p /localstore/data
docker@minikube:~$ sudo chmod 777 /localstore/data
docker@minikube:/localstore/data$ echo "Hello from local K8s volume" > /localstore/data/index.html
docker@minikube:/localstore/data$ cat /localstore/data/index.html
Hello from local K8s volume
docker@minikube:~$ exit
logoutCreate StorageClass
Save the following YAML file in your directory.
File: k8s-volumes-storageclass-local.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumerCreate the StorageClass using kubectl apply -f YAML_FILE.
~/learnk8s> kubectl get storageclass
NAME PROVISIONER RECLAIMPOLICY VOLUMEBINDINGMODE ALLOWVOLUMEEXPANSION AGE
local-storage kubernetes.io/no-provisioner Delete WaitForFirstConsumer false 26s
standard (default) k8s.io/minikube-hostpath Delete Immediate false 3dCreate a PersistentVolume
Save the following YAML file in your directory.
File: k8s-volumes-pv-local.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
name: demo-pv
labels:
type: demo-pv
spec:
storageClassName: local-storage # name of StorageClass to which this pv belongs
capacity:
storage: 1Gi
accessModes:
- ReadWriteOnce
local: # directly-attached storage with node affinity
path: /localstore/data # full path to the volume on the node
nodeAffinity:
required:
nodeSelectorTerms:
- matchExpressions: # kubectl get nodes --show-labels
- key: kubernetes.io/hostname
operator: In
values:
- "minikube"Create the PV using kubectl apply -f YAML_FILE.
~/learnk8s> kubectl apply -f yaml/k8s-volumes-pv-local.yaml
persistentvolume/demo-pv created
~/learnk8s> kubectl get pv demo-pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
demo-pv 1Gi RWO Retain Available local-storage 18s
~/learnk8s>The output shows that the PersistentVolume has a STATUS of Available. This means it has not yet been bound to a PersistentVolumeClaim.
Create a PersistentVolumeClaim
Save the following YAML file in your directory.
File: k8s-volumes-pvc-local.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: demo-pvc
spec:
resources: # minimum resources the volume should have
requests: # minimum amount of compute resources required
storage: 1Gi
accessModes:
- ReadWriteOnce
storageClassName: local-storage # StorageClass required by the claimCreate the PVC using kubectl apply -f YAML_FILE.
~/learnk8s> kubectl apply -f yaml/k8s-volumes-pvc-local.yaml
persistentvolumeclaim/demo-pvc created
~/learnk8s> kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
demo-pvc Pending local-storage 5sThe output shows that the PersistentVolumeClaim has a STATUS of Pending. We can run kubectl describe to see why.
~/learnk8s> kubectl describe pvc demo-pvc
Name: demo-pvc
Namespace: default
StorageClass: local-storage
Status: Pending
Volume:
Labels: <none>
Annotations: <none>
Finalizers: [kubernetes.io/pvc-protection]
Capacity:
Access Modes:
VolumeMode: Filesystem
Used By: <none>
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal WaitForFirstConsumer 13s (x6 over 84s) persistentvolume-controller waiting for first consumer to be created before bindingCreate a Pod
Create a Pod that uses your PersistentVolumeClaim as a volume.
Save the following YAML file in your directory.
Notice that the Pod's configuration file specifies a PersistentVolumeClaim, but it does not specify a PersistentVolume. From the Pod's point of view, the claim is a volume.
File: k8s-volumes-pod-pv.yaml
apiVersion: v1
kind: Pod
metadata:
name: demo-pv-pod
# namespace: devns
spec: # PodSpec
volumes: # List of volumes that can be mounted by containers belonging to the pod
- name: pv-storage
persistentVolumeClaim:
claimName: demo-pvc
containers:
- name: demo-pv-container
image: nginx
resources:
limits:
memory: "128Mi"
cpu: "500m"
ports:
- containerPort: 80
volumeMounts: # Pod volumes to mount into the container's filesystem
- mountPath: /usr/share/nginx/html
name: pv-storage # This must match the Name of a VolumeCreate the Pod using kubectl apply -f YAML_FILE.
~/learnk8s> kubectl apply -f yaml/k8s-volumes-pod-pv.yaml
pod/demo-pv-pod created
~/learnk8s> kubectl get pod demo-pv-pod
NAME READY STATUS RESTARTS AGE
demo-pv-pod 1/1 Running 0 7sLook at the PV and PVC.
~/learnk8s> kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
demo-pvc Bound demo-pv 1Gi RWO local-storage 7m4s
~/learnk8s> kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
demo-pv 1Gi RWO Retain Bound default/demo-pvc local-storage 10mThe output shows that the PVC is now bound to the PV.
Verification
Get a shell to the container running in your Pod. In your shell, verify that nginx is serving the index.html file from the local volume:
~/learnk8s> kubectl apply -f yaml/k8s-volumes-pod-pv.yaml
pod/demo-pv-pod created
~/learnk8s> kubectl get pod demo-pv-pod
NAME READY STATUS RESTARTS AGE
demo-pv-pod 1/1 Running 0 32s
~/learnk8s> kubectl exec -it demo-pv-pod -- /bin/bash
root@demo-pv-pod:/# curl localhost
Hello from local K8s volume
root@demo-pv-pod:/# exit
exit
~/learnk8s>Cleanup
Delete the Pod, PVC, PV, StorageClass.
~/learnk8s> kubectl delete pod demo-pv-pod
pod "demo-pv-pod" deleted
~/learnk8s> kubectl delete pvs demo-pvc
error: the server doesn't have a resource type "pvs"
~/learnk8s> kubectl delete pvc demo-pvc
persistentvolumeclaim "demo-pvc" deleted
~/learnk8s> kubectl delete pv demo-pv
persistentvolume "demo-pv" deleted
~/learnk8s> kubectl delete storageclass local-storage
storageclass.storage.k8s.io "local-storage" deletedIn the shell on your Node, remove the file and directory that you created.
~/learnk8s> minikube ssh
Last login: Tue May 30 21:51:32 2023 from 192.168.58.1
docker@minikube:~$
docker@minikube:/$ sudo rm -rf /localstore/
docker@minikube:~$ exit
logout