A. Volume (in pod)

• by-default pop are transient. data in not retained after pod is terminated.
• how to persist data processed by the containers.
• sol - Volume
• 
• volume Types:
• emptyDir - Temporary storage created when a pod starts, Deleted when the pod is terminated
• nfs: Mounts a remote NFS server directory into the pod.
• awsElasticBlockStore / gcePersistentDisk / azureDisk
• csi : third-party storage providers to integrate with Kubernetes
• hostpath - mount File or directory from the host node's filesystem into a pod
• 
• Create volume and mount it in single pod.
  

  apiVersion: v1
  kind: Pod                       <<<<<
  metadata:
      name: 
  spec:
      containers:
      - ...
        volumeMounts:
          - mountPath: /opt
            name: data-volume
  
      volumes:                    <<<<<< CONFIGURED VOLUME WITHIN POD
      - name: data-volume
        hostPath:                 # source-1 - Node local dir
          path: /data
          type: Directory
        ---- OR ----
        awsElasticBlockStore:     # source-2 - aws EBS
          volumeID: 
          fsType:   
  

---

B. Central Volume

• 

PV - Persistent Volume

• having multiple pod, then maintain storage centrally
• and carve out part of to each pod using claims (PVC)
• usually admin creates PV. and user creates PVC

  apiVersion: v1
  kind: PersistentVolume
  metadata:
      name: pv-vol1
  spec: 
      accessModes:   # how to mount
      - ReadWriteOnce  # ReadOnlyMany,  ReadWriteOnce,  ReadWriteMany
      capacity:
          storage: 1Gi
      hostPath:                   # source-1
          path: /tmp/da
      ---- OR ----    
      awsElasticBlockStore:       # source-2
          volumeID: 
          fsType:
      ---- OR ----    
      azureDisk:
          ...    
  

---

PVC - Persistent Volume claims

• request for binding to storage/PV based on :
• capacity
• accessMode/s
• volume Modes
• storage class
• labels and selectors.
• 1-to-1 b/w PV and PVC
• once a PV is bind
• then no other PVC will get bind to that PV>
• smaller PVC can get binded to big PV (if thats the only match)
• state: pending + bind
• if delete PVC, then PV is retain (by default). even data inside PV
• pesistentVolumeClaimPolicy: Retain
• options:
  • retain - keep PV with data (default)
  • Delete - delete PV
  • recycle - keep PV only, scrap all Data
• definition:
• we don't define binding in definition

• it just finds matching one at runtime. <<<<

    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
        name: myclaim
    spec:
      # storageClassName: 
      accessModes:
        - ReadWriteOnce
      resources:
        requests:           <<< request
          storage: 500Mi
          ...
          ... 
  

• Next, use it inside - pod, deployment and RS object

  # pod,RS,D object:
  spec:
     ...
     ...    
     volumes:
     - name: mypd
       persistentVolumeClaim:
         claimName: myclaim
  

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Screenshots:

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