Understanding emptyDir and local Volumes in Kubernetes

 

Overview

Kubernetes provides different volume types depending on how long data should live and where it should live.
Two commonly confused options are:

• emptyDir
• local Persistent Volumes

Although both rely on node storage, they behave very differently in terms of lifecycle, scope, and production suitability.

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emptyDir: Pod-Level Ephemeral Storage

What is emptyDir?

emptyDir is an ephemeral volume that exists only for the lifetime of a Pod.

• Created when a Pod is scheduled to a node
• Deleted as soon as the Pod is removed
• Initially empty
• Shared between all containers inside the same Pod

Data strictly follows the Pod lifecycle.

Key Characteristics

• Scoped to one Pod
• Cannot be shared across Pods
• Data is lost when:
  • Pod is deleted
  • Pod is rescheduled to another node

Typical Use Cases

• Sharing temporary files between containers
• Caching data
• Scratch space
• Temporary processing artifacts

Example

apiVersion: v1
kind: Pod
metadata:
  name: example-emptydir
spec:
  containers:
    - name: app
      image: busybox
      command: ["sh", "-c", "echo hello > /data/file.txt && sleep 3600"]
      volumeMounts:
        - name: cache
          mountPath: /data
  volumes:
    - name: cache
      emptyDir: {}

---

local Volumes: Node-Level Persistent Storage

What is a Local Volume?

A local volume is a PersistentVolume backed by local disk on a specific node.

• Data survives Pod restarts
• Data is tied to one specific node
• Data is lost if the node is removed or replaced

Data follows the Node lifecycle, not the Pod lifecycle.

Key Characteristics

• Requires a PersistentVolume
• Requires a PersistentVolumeClaim
• Node affinity is mandatory
• Supports static provisioning only
• Pod must always run on the same node

Example PersistentVolume

apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage
  local:
    path: /mnt/disks/data
  nodeAffinity:
    required:
      nodeSelectorTerms:
        - matchExpressions:
            - key: kubernetes.io/hostname
              operator: In
              values:
                - node-1

Example PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: local-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: local-storage

---

Lifecycle Comparison

Feature	emptyDir	local volume
Scope	Pod	Node
Persistence	❌ No	✅ Yes (node-bound)
Requires PVC	❌ No	✅ Yes
Node Affinity	❌ No	✅ Mandatory
Survives Pod restart	❌ No	✅ Yes
Survives Node loss	❌ No	❌ No
Provisioning	Dynamic	Static only

---

Production Considerations

⚠️ Important

Neither emptyDir nor local volumes are recommended for critical production data.

• emptyDir → data disappears with the Pod
• local → data disappears with the Node

When They Make Sense

Volume	When to Use
emptyDir	Temporary files, cache, IPC between containers
local	Performance-sensitive workloads where data loss is acceptable

For real persistence, prefer:

• Network storage (NFS, iSCSI)
• Cloud volumes (EBS, PD, Azure Disk)
• CSI-based storage solutions

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Key Takeaway

Always think in terms of data lifecycle.

• Pod lifecycle → emptyDir
• Node lifecycle → local volume

If losing the data is not acceptable, do not use either.