Concept

![[images/截屏2026-03-24 16.45.32.png]]

A Volume can be used to hold data and state for Pods and containers.

A Pod can have multiple Volumes attached to it.
Containers rely on a mountPath to access a volume.

Storage Types

Volumes
PersistentVolumes
PersistentVolumeClaims
StorageClasses

Volumes

A Volume references a storage location
Must have a unique name
Attached to a Pod and may or may not be tied to the Pod’s lifetime (depending on the Volume type)
A Volume Mount references a Volume by name and defines a mountPath

Volume Types

emptyDir: Empty directory for storing transient data (shares a Pod’s lifetime) useful for sharing files between containers running in a Pod. (Ephemeral storage)
hostPath: Pod mounts into the node’s filesystem.
Network File System (nfs): An NFS share mounted into the Pod.
configMap/secret: Special types of volumes that provide a Pod with access to Kubernetes resources.
persistentVolumeClaim: Provides Pods with a more persistent storage option that is abstracted from the details.
cloud: Cluster-wide storage

emptyDir Volume

apiVersion: v1
kind: Pod
metadata:
  name: nginx-alpine-volume
spec:
  containers:
  - name: nginx
    image: nginx:alpine
    volumeMounts:
      - name: html
        mountPath: /usr/share/nginx/html
        readOnly: true
    resources:
  - name: html-updater
    image: alpine
    command: ["/bin/sh", "-c"]
    args:
      - while true; do date >> /html/index.html;sleep 10; done
    resources:
    volumeMounts:
      - name: html
        mountPath: /html
  volumes:
  - name: html
    emptyDir: {} #lifecycle tied to Pod

# kubectl apply -f nginx-alpine-emptyDir.pod.yml
# kubectl port-forward nginx-alpine-volume 8080:80

![[images/截屏2026-03-24 17.14.14.png]]

hostPath Volume

apiVersion: v1
kind: Pod
metadata:
  name: docker-volume
spec:
  containers:
  - name: docker
    image: docker
    command: ["sleep"]
    args: ["100000"]
    volumeMounts:
    - name: docker-socket
      mountPath: /var/run/docker.sock
    resources:
  volumes:
  - name: docker-socket
    hostPath:
      path: /var/run/docker.sock
      type: Socket

# Once Pod is created you can shell into it to run Docker commands:
# kubectl exec [pod-name] -it -- sh

Valid types includes:

DirectoryOrCreate
Directory
FileOrCreate
File
Socket
CharDevice
BlockDevice

![[images/截屏2026-03-24 17.22.15.png]]

Cloud Volumes

Cloud providers support different types of Volumes:

Azure: Azure Disk and Azure File
AWS: Elastic Block Store
GCP: GCE Persistent Disk

![[images/截屏2026-03-24 17.26.28.png]]

![[images/截屏2026-03-24 17.27.06.png]]

![[images/截屏2026-03-24 17.27.29.png]]

Check

kubectl describe pod [pod_name]
# Get Pod YAML
kubectl get pod [pod_name] -o yaml

PersistentVolumes and PersistentVolumeClaims

A PersistentVolume (PV) is a cluster-wide storage unit provisioned by an administrator with a lifecycle independent from a Pod.

A PersistentVolumeClaim (PVC) is a request for a storage unit (PV).

![[images/截屏2026-03-25 15.14.44.png]]

A PersistentVolume is a cluster-wide storage resource that relies on network-attached storage (NAS).
Normally provisioned by a cluster administrator.
Available to a Pod even if it gets rescheduled to a different Node.
Rely on a storage provider such as NFS, cloud storage, or other options.
Associated with a Pod by using a PersistentVolumeClaim.

PersistentVolume Workflow

Create network storage resource (NFS, cloud, …)
Define a PV and send to the Kubernetes API
Create a PVC
Kubernetes binds the PVC to the PV
Pod Volume references the PVC

![[images/截屏2026-03-25 15.18.40.png]]

YAML

Create PV

![[images/截屏2026-03-25 15.22.06.png]]

Create PVC

![[images/截屏2026-03-25 15.22.55.png]]

Create Reference

![[images/截屏2026-03-25 15.24.08.png]]

StorageClasses

A StorageClasses (SC) is a type of storage template that can be used to dynamically provision storage.

![[images/截屏2026-03-25 15.25.59.png]]

Used to define different classes of storage
Act as a type of storage template
Supports dynamic provisioning of PersistentVolumes
Don’t need to create PV in advance

StorageClass Workflow

Create Storage Class
Create PVC referencing to SC
Kubernetes uses SC provisioner to provision a PV
Storage provisioned, PV created and bound to PVC
Pod volume references PVC

![[images/截屏2026-03-25 15.29.41.png]]

YAML

Define SC

![[images/截屏2026-03-25 15.31.02.png]]

Define PV

![[images/截屏2026-03-25 15.32.48.png]]

Define PVC

![[images/截屏2026-03-25 15.33.50.png]]

![[images/截屏2026-03-25 15.34.15.png]]

Mongo Example

apiVersion: v1
kind: ConfigMap
metadata:
  labels:
    app: mongo-env
  name: mongo-env
data:
  MONGODB_DBNAME: codeWithDan
  #NO - not a good idea to store a password in a ConfigMap (demo only). See the "secrets" folder for another demo of this.
  MONGODB_PASSWORD: password 
  MONGODB_ROLE: readWrite
  #NO - not a good idea to store a password in a ConfigMap (demo only). See the "secrets" folder for another demo of this.
  MONGODB_ROOT_PASSWORD: password
  MONGODB_ROOT_ROLE: root
  MONGODB_ROOT_USERNAME: dbadmin
  MONGODB_USERNAME: webrole

---

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
# The reclaim policy applies to the persistent volumes not the storage class itself. 
# pvs and pvcs that are created using that storage class will inherit the reclaim policy set here.
reclaimPolicy: Retain
volumeBindingMode: WaitForFirstConsumer

---

# Note: While a local storage PV works, going with a more durable solution (NFS, cloud option, etc.) is recommended
# Adding this for demo purposes to run on Docker Desktop Kubernetes since it only supports a single Node
# https://kubernetes.io/blog/2018/04/13/local-persistent-volumes-beta/
apiVersion: v1
kind: PersistentVolume
metadata:
  name: mongo-pv
spec:
  capacity:
    storage: 1Gi
  volumeMode: Filesystem
  accessModes:
  - ReadWriteOnce
  # StorageClass has a reclaim policy default so it'll be "inherited" by the PV
  # persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage
  hostPath:
    path: /private/tmp/data/db
    type: DirectoryOrCreate
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - docker-desktop

---

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mongo-pvc
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: local-storage
  resources:
    requests:
      storage: 1Gi

---

apiVersion: v1
kind: Service
metadata:
  name: mongo
spec:
  selector:
    app: mongo
  ports:
  - port: 27017
    targetPort: 27017

---

apiVersion: apps/v1
kind: StatefulSet
metadata:
  labels:
    app: mongo
  name: mongo
spec:
  serviceName: mongo
  replicas: 1
  selector:
    matchLabels:
      app: mongo
  template:
    metadata:
      labels:
        app: mongo
    spec:
      containers:
        - image: mongo
          name: mongo
          ports:
          - containerPort: 27017
          command:
          - mongod
          - "--auth"
          resources: {}        
          volumeMounts:
          - name: mongo-volume
            mountPath: /data/db
          env:
            - name: MONGODB_DBNAME
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_DBNAME
                  name: mongo-env
            - name: MONGODB_PASSWORD
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_PASSWORD
                  name: mongo-env
            - name: MONGODB_ROLE
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_ROLE
                  name: mongo-env
            - name: MONGODB_ROOT_PASSWORD
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_ROOT_PASSWORD
                  name: mongo-env
            - name: MONGODB_ROOT_ROLE
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_ROOT_ROLE
                  name: mongo-env
            - name: MONGODB_ROOT_USERNAME
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_ROOT_USERNAME
                  name: mongo-env
            - name: MONGODB_USERNAME
              valueFrom:
                configMapKeyRef:
                  key: MONGODB_USERNAME
                  name: mongo-env
      volumes:
      - name: mongo-volume
        persistentVolumeClaim:
          claimName: mongo-pvc