Volumes

Overview

Volumes provide persistent and shared storage for containers in a pod.

---

Volume Types

Type	Description	Persistence
emptyDir	Temp directory, deleted with pod	Pod lifetime
hostPath	Mount from node filesystem	Node
configMap	Mount ConfigMap as files	Cluster
secret	Mount Secret as files	Cluster
persistentVolumeClaim	Mount PVC	Persistent
downwardAPI	Mount pod metadata	Pod lifetime

---

emptyDir

Temporary storage, shared between containers:

apiVersion: v1
kind: Pod
metadata:
  name: emptydir-demo
spec:
  containers:
  - name: writer
    image: busybox
    command: ["sh", "-c", "echo hello > /data/file && sleep 3600"]
    volumeMounts:
    - name: shared-data
      mountPath: /data
  - name: reader
    image: busybox
    command: ["sh", "-c", "cat /data/file && sleep 3600"]
    volumeMounts:
    - name: shared-data
      mountPath: /data
  volumes:
  - name: shared-data
    emptyDir: {}

emptyDir in Memory

volumes:
- name: cache
  emptyDir:
    medium: Memory      # Use RAM instead of disk
    sizeLimit: 100Mi

---

hostPath

Mount directory from node:

apiVersion: v1
kind: Pod
metadata:
  name: hostpath-demo
spec:
  containers:
  - name: app
    image: busybox
    command: ["sh", "-c", "cat /host-logs/* && sleep 3600"]
    volumeMounts:
    - name: logs
      mountPath: /host-logs
      readOnly: true
  volumes:
  - name: logs
    hostPath:
      path: /var/log
      type: Directory

hostPath Types

Type	Description
""	No check
DirectoryOrCreate	Create if missing
Directory	Must exist
FileOrCreate	Create file if missing
File	Must exist

---

ConfigMap as Volume

apiVersion: v1
kind: Pod
metadata:
  name: configmap-volume
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: config-vol
      mountPath: /etc/config
  volumes:
  - name: config-vol
    configMap:
      name: app-config

Mount Specific Keys

volumes:
- name: config-vol
  configMap:
    name: app-config
    items:
    - key: app.properties
      path: application.properties
    - key: logging.conf
      path: log.conf

---

Secret as Volume

apiVersion: v1
kind: Pod
metadata:
  name: secret-volume
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: secret-vol
      mountPath: /etc/secrets
      readOnly: true
  volumes:
  - name: secret-vol
    secret:
      secretName: app-secrets

---

PersistentVolumeClaim

apiVersion: v1
kind: Pod
metadata:
  name: pvc-demo
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: data
      mountPath: /usr/share/nginx/html
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: my-pvc

---

subPath

Mount specific file/directory without overwriting:

volumeMounts:
- name: config-vol
  mountPath: /etc/nginx/nginx.conf
  subPath: nginx.conf    # Only mount this file

---

Multiple Mounts

spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: config
      mountPath: /etc/config
    - name: secrets
      mountPath: /etc/secrets
    - name: data
      mountPath: /data
  volumes:
  - name: config
    configMap:
      name: app-config
  - name: secrets
    secret:
      secretName: app-secrets
  - name: data
    persistentVolumeClaim:
      claimName: my-pvc

---

Read-Only Mount

volumeMounts:
- name: secrets
  mountPath: /etc/secrets
  readOnly: true

---

Useful Commands

# Check mounted volumes
kubectl describe pod <pod-name> | grep -A10 "Volumes"

# Verify mount inside pod
kubectl exec <pod-name> -- ls -la /path/to/mount
kubectl exec <pod-name> -- df -h