Why persistent storage matters in Kubernetes - See It in Action

Why persistent storage matters in Kubernetes

📖 Scenario: You are managing a Kubernetes cluster that runs applications needing to save data permanently. You want to understand how to set up storage that keeps data safe even if containers restart or move.

🎯 Goal: Learn how to create a PersistentVolumeClaim in Kubernetes and use it in a Pod to keep data persistent across container restarts.

📋 What You'll Learn

Create a PersistentVolumeClaim named my-pvc requesting 1Gi of storage

Create a Pod named storage-demo that uses the my-pvc volume

Mount the volume inside the Pod at /data

Verify the Pod can write and read data from the persistent volume

💡 Why This Matters

🌍 Real World

Applications like databases, content management systems, and file servers need persistent storage to keep data safe even if containers restart or move to other nodes.

💼 Career

Understanding persistent storage in Kubernetes is crucial for DevOps engineers and cloud administrators to ensure data durability and application reliability.

1

Create a PersistentVolumeClaim

Write a YAML manifest to create a PersistentVolumeClaim named my-pvc that requests 1Gi of storage with access mode ReadWriteOnce.

Kubernetes

# Write the PersistentVolumeClaim YAML manifest here
# Your code here

Hint

Use kind: PersistentVolumeClaim and specify storage: 1Gi under resources.requests.

2

Create a Pod that uses the PersistentVolumeClaim

Write a YAML manifest to create a Pod named storage-demo that mounts the PersistentVolumeClaim my-pvc as a volume named mypvc-volume inside the container at path /data. Use the image busybox and keep the container running with sleep 3600.

Kubernetes

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

# Write the Pod YAML manifest here
# Your code here

Hint

Define a Pod with a container that mounts the volume from my-pvc at /data.

3

Write data inside the Pod to the persistent volume

Use kubectl exec to run the command echo 'Hello Kubernetes' > /data/message.txt inside the storage-demo Pod to write data to the persistent volume.

Kubernetes

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
---
apiVersion: v1
kind: Pod
metadata:
  name: storage-demo
spec:
  containers:
  - name: busybox
    image: busybox
    command: ["sleep", "3600"]
    volumeMounts:
    - name: mypvc-volume
      mountPath: /data
  volumes:
  - name: mypvc-volume
    persistentVolumeClaim:
      claimName: my-pvc

# Run the kubectl exec command below
# Your code here

Hint

Use kubectl exec with sh -c to write the text into /data/message.txt.

4

Read the data back from the persistent volume

Use kubectl exec to run cat /data/message.txt inside the storage-demo Pod and print the output to verify the data is saved persistently.

Kubernetes

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
---
apiVersion: v1
kind: Pod
metadata:
  name: storage-demo
spec:
  containers:
  - name: busybox
    image: busybox
    command: ["sleep", "3600"]
    volumeMounts:
    - name: mypvc-volume
      mountPath: /data
  volumes:
  - name: mypvc-volume
    persistentVolumeClaim:
      claimName: my-pvc

kubectl exec storage-demo -- sh -c "echo 'Hello Kubernetes' > /data/message.txt"

# Run the kubectl exec command to read the file below
# Your code here

Hint

Use kubectl exec storage-demo -- cat /data/message.txt to read and print the file content.

Practice

1. Why is persistent storage important in Kubernetes?

easy

A. It speeds up container startup time

B. It manages network traffic between pods

C. It automatically scales the number of pods

D. It keeps data safe even if containers stop or restart

Solution

1. Step 1: Understand container lifecycle

   Containers can stop or restart anytime, losing any data stored inside them.

2. Step 2: Role of persistent storage

   Persistent storage keeps data safe beyond container life, so data is not lost.

3. Final Answer:

   It keeps data safe even if containers stop or restart -> Option D

4. Quick Check:

   Persistent storage = data safety beyond containers [OK]

Hint: Persistent storage saves data beyond container life [OK]

Common Mistakes:

• Thinking persistent storage speeds up containers
• Confusing storage with network management
• Assuming storage auto-scales pods

2. Which of the following is the correct way to request persistent storage in Kubernetes?

easy

A. kubectl get storageclass

B. kubectl create pod --storage

C. kubectl apply -f persistentvolumeclaim.yaml

D. kubectl delete pvc

Solution

1. Step 1: Identify how to request storage

   PersistentVolumeClaim (PVC) is used to request storage in Kubernetes.

2. Step 2: Correct command to apply PVC

   Using kubectl apply -f persistentvolumeclaim.yaml applies the PVC configuration.

3. Final Answer:

   kubectl apply -f persistentvolumeclaim.yaml -> Option C

4. Quick Check:

   Request storage with PVC YAML and apply [OK]

Hint: Use kubectl apply with PVC YAML to request storage [OK]

Common Mistakes:

• Using pod creation command to request storage
• Confusing storageclass listing with requesting storage
• Deleting PVC instead of creating it

3. Given this PersistentVolumeClaim YAML snippet:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

What does ReadWriteOnce mean?

medium

A. The volume can be mounted as read-write by only one pod at a time

B. The volume is automatically deleted when pod stops

C. The volume is read-only for all pods

D. The volume can be mounted as read-write by many pods simultaneously

Solution

1. Step 1: Understand accessModes in PVC

   AccessModes define how many pods can mount the volume and with what permissions.

2. Step 2: Meaning of ReadWriteOnce

   ReadWriteOnce means only one pod can mount the volume as read-write at a time.

3. Final Answer:

   The volume can be mounted as read-write by only one pod at a time -> Option A

4. Quick Check:

   ReadWriteOnce = single pod read-write mount [OK]

Hint: ReadWriteOnce means single pod read-write access [OK]

Common Mistakes:

• Thinking ReadWriteOnce allows multiple pods
• Confusing read-only with ReadWriteOnce
• Assuming volume auto-deletes with pod

4. You created a PersistentVolumeClaim but your pod fails to mount the volume with error "volume not found". What is the most likely cause?

medium

A. The PersistentVolumeClaim name does not match the volume name in the pod spec

B. The pod spec is missing the container image

C. The PersistentVolumeClaim requested storage size is too small

D. The pod is missing resource limits

Solution

1. Step 1: Check volume mount configuration

   The pod must reference the PVC by the exact name to mount the volume.

2. Step 2: Identify cause of "volume not found" error

   If names don't match, Kubernetes cannot find the volume to mount.

3. Final Answer:

   The PersistentVolumeClaim name does not match the volume name in the pod spec -> Option A

4. Quick Check:

   Volume mount fails if PVC name mismatches [OK]

Hint: Match PVC name exactly in pod volume spec [OK]

Common Mistakes:

• Ignoring volume name mismatch
• Blaming container image for volume errors
• Assuming storage size causes mount failure

5. You want two pods to share the same persistent storage volume with read-write access at the same time. Which access mode should you specify in your PersistentVolumeClaim?

hard

A. ReadWriteOnce

B. ReadWriteMany

C. ReadOnlyMany

D. WriteOnce

Solution

1. Step 1: Understand access modes for sharing

   ReadWriteMany allows multiple pods to mount the volume as read-write simultaneously.

2. Step 2: Choose correct access mode for sharing

   Since two pods need read-write access at the same time, ReadWriteMany is required.

3. Final Answer:

   ReadWriteMany -> Option B

4. Quick Check:

   Multiple pods read-write = ReadWriteMany [OK]

Hint: Use ReadWriteMany for shared read-write access [OK]

Common Mistakes:

• Using ReadWriteOnce which allows only one pod
• Confusing ReadOnlyMany with read-write access
• Selecting non-existent WriteOnce mode