How to persist volumes in k8s?

read - https://kubernetes.io/docs/concepts/storage/persistent-volumes/

things to know

• persistent volume is like a huge disk running in the cluster
• while persistent volume claim is like a small piece of the persistent volume claimed by an application in the cluster
• volumes are just like any other k8s resource ex pods, nodes, etc.
• can be provisioned beforehand or dynamically

how to create a PersistentVolumeClaim?

storage.yaml - creates a persistent volume claim named mealie-data in the mealie namespace of the cluster

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mealie-data
  namespace: mealie
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 500Mi

deployment.yaml - the persistent volume claim is being used by the deployment by mounting it to a certain path in the pod ex- /app/data

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: mealie
  name: mealie
  namespace: mealie
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mealie
  template:
    metadata:
      labels:
        app: mealie
    spec:
      containers:
        - image: ghcr.io/mealie-recipes/mealie:v3.1.2
          name: mealie
          ports:
            - containerPort: 9000
          volumeMounts:
            - mountPath: /app/data
              name: mealie-data
      volumes:
        - name: mealie-data
          persistentVolumeClaim:
            claimName: mealie-data

• once a persistent volume is created and a persistent volume claim is made in the deployment, even if we delete the deployment, the data is going to persist when we restart it!
• also we have the liberty to mount this pvc to any other pod and access it there!

amazing ain’t it! 😍

where is k8s storing the data actually?

• when we talk of persistent volumes where does k8s actually store the data???!
• that’s where storage classes come into play, it defines where the cluster is supposed to store the data - in local storage, cloud, or some place else

❯ k get storageclasses.storage.k8s.io
NAME                   PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
local-path (default)   rancher.io/local-path   Delete          WaitForFirstConsumer   false                  12d

• in rancher desktop it is local-path by default and hence the data is stored in the local machine
• read more about storage classes - https://kubernetes.io/docs/concepts/storage/storage-classes/

Links:

k8s storage

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