Day 29/40
Kubernetes Volume Simplified | Persistent Volume, Persistent Volume Claim & Storage Class
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@piyushsachdeva
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My Git Repo
This section is about pv persistent volume, pvc persistent volume claim, storage class and some other concepts about storage.
Let's assume a pod like the below, which has a volume named redis-storage and an emptyDir that is not persistent because we don't mount it somewhere.
apiVersion: v1
kind: Pod
metadata:
name: redis-pod
spec:
containers:
- image: redis
name: redis
volumeMounts:
- name: redis-storage
mountPath: /data/redis
volumes:
- name: redis-storage
emptyDir: {}
root@localhost:~# kubectl apply -f day29-storage.yaml
pod/redis-pod created
root@localhost:~# kubectl get pods
NAME READY STATUS RESTARTS AGE
redis-pod 1/1 Running 0 10s
root@localhost:~# kubectl exec -it redis-pod -- bash
root@redis-pod:/data# mount | grep redis
/dev/vda1 on /data/redis type ext4 (rw,relatime,discard,errors=remount-ro)
If the pod killed or restarted, the data is still persist, but if the pod deleted, the data will be lost.
At first we need some definitions to have better understanding the concepts.
source
Volume: In
Kubernetes,volumeabstractions are used to provide an API that abstracts the physical implementation ofstoragefrom how it is consumed by application resources.
Kubernetes supports two major types of Volumes:
- Ephemeral Volumes - These are used for applications that need storage but do not need to access the data after a restart:
- emptyDir
- Secrets, ConfigMaps and the downwardAPI
- CSI (Container Storage Interface) Ephemeral Volumes
- Generic Ephemeral Volumes
- Persistent Volumes - This is an API object that represents an abstract implementation of physical storage to be used by PODs, but they last beyond a POD’s lifetime.
Persistent Storage: Once a CSI plugin has been set up and is running in Kubernetes, resources and users can consume volumes using the Kubernetes Storage API objects:
Persistent Volumes,Persistent Volume ClaimsandStorage Classes.
- **Persistent Volumes (PV)**: is a piece of `storage` available to the `cluster`. The `PV` exposes object, file and block storage systems by capturing the details of its implementation protocol, be it `iSCSI` (SCSI over Internet), `NFS` or any storage systems offered by specific vendors and cloud providers. The `Persistent Volume` has its lifecycle independent of any `POD` consuming it.
- **Persistent Volume Claims (PVC)**: When a user requests for `PV` storage, they use a `Persistent Volume Claim` as a `Kubernetes` object that requests specific storage requirements such as `access modes` and size.
The Lifecycle of
PVs andPVCs:
- Provisioning
- Binding
- Using
- Reclaiming
Reclaim Policy:
- Retain
- Delete
- Recycle
Some of the most popular CSI Plugins for Kubernetes include:
- AWS Elastic Block Storage
- Azure disk
- BeeGFS
- CephFS
- Dell EMC PowerMax
- GCE Persistent Disk
- Google Cloud Filestore
- GlusterFS
- Huawei Storage CSI
- HyperV CSI
- IBM Block Storage
- OpenEBS
- Portworx
- Pure Storage CSI
The complete list is here
- Access Mode:
- ReadWriteOnce - the volume can be mounted as read-write by a single node.
- ReadOnlyMany - the volume can be mounted as read-only by many nodes.
- ReadWriteMany - the volume can be mounted as read-write by many nodes.
- ReadWriteOncePod - the volume can be mounted as read-write by a single Pod. source
(Photo from the video)
Demo
based on the diagram
1. Create a PV
apiVersion: v1
kind: PersistentVolume
metadata:
name: task-pv-volume
labels:
type: local
spec:
storageClassName: standard
capacity:
storage: 1Gi
accessModes:
- ReadWriteOnce
hostPath:
path: "/home/day29"
root@localhost:~# kubectl apply -f day29-pv.yaml
persistentvolume/task-pv-volume created
root@localhost:~# kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS VOLUMEATTRIBUTESCLASS REASON AGE
task-pv-volume 1Gi RWO Retain Available <unset> 10s
1. Create a PVC
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: task-pv-claim
spec:
storageClassName: standard
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 500Mi
root@localhost:~# kubectl apply -f day29-pvc1.yaml
persistentvolumeclaim/task-pv-claim created
root@localhost:~# kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS VOLUMEATTRIBUTESCLASS REASON AGE
task-pv-volume 1Gi RWO Retain Available <unset> 4m4s
root@localhost:~# kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS VOLUMEATTRIBUTESCLASS AGE
task-pv-claim Pending standard <unset> 19s
It remains in Pending status until a pod would claim it.
apiVersion: v1
kind: Pod
metadata:
name: task-pv-pod
spec:
volumes:
- name: task-pv-storage
persistentVolumeClaim:
claimName: task-pv-claim
containers:
- name: task-pv-container
image: nginx
ports:
- containerPort: 80
name: "http-server"
volumeMounts:
- mountPath: "/usr/share/nginx/html"
name: task-pv-storage
root@localhost:~# kubectl get pod
NAME READY STATUS RESTARTS AGE
task-pv-pod 1/1 Running 0 9s
root@localhost:~# kubectl get pv
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS VOLUMEATTRIBUTESCLASS REASON AGE
task-pv-volume 1Gi RWO Retain Bound default/task-pv-claim standard <unset> 32s
root@localhost:~# kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS VOLUMEATTRIBUTESCLASS AGE
task-pv-claim Bound task-pv-volume 1Gi RWO standard <unset> 24s
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