Storage classes for dynamic provisioning in Kubernetes - Commands & Configuration

Introduction

When you need storage for your applications in Kubernetes, you can create it automatically using storage classes. This saves you from manually setting up storage every time. Storage classes tell Kubernetes how to create storage on demand.

When you want your app to get storage automatically without manual setup.

When you need different types of storage like fast SSD or cheaper HDD for different apps.

When you want to manage storage policies like encryption or replication easily.

When you want to avoid errors from manually creating storage volumes.

When you want to scale storage dynamically as your app grows.

Config File - storageclass.yaml

storageclass.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-storage
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
  fsType: ext4
reclaimPolicy: Delete
volumeBindingMode: Immediate

This file defines a StorageClass named fast-storage. It uses the AWS Elastic Block Store (EBS) provisioner to create gp2 type volumes formatted with ext4 filesystem. The reclaimPolicy: Delete means storage is deleted when no longer used. volumeBindingMode: Immediate means volumes are created right when requested.

Commands

This command creates the StorageClass in your Kubernetes cluster so it can be used for dynamic storage provisioning.

Terminal

kubectl apply -f storageclass.yaml

Expected Output

storageclass.storage.k8s.io/fast-storage created

This command lists all StorageClasses available in the cluster to verify that your new StorageClass was created.

Terminal

kubectl get storageclass

Expected Output

NAME           PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE

fast-storage   kubernetes.io/aws-ebs   Delete         Immediate           false                  10s

This command creates a PersistentVolumeClaim that requests storage using the StorageClass named fast-storage. Kubernetes will dynamically create the storage volume.

Terminal

kubectl apply -f pvc.yaml

Expected Output

persistentvolumeclaim/my-pvc created

This command checks the status of the PersistentVolumeClaim to see if the storage has been successfully provisioned and bound.

Terminal

kubectl get pvc my-pvc

Expected Output

NAME     STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE

my-pvc   Bound    pvc-12345678-90ab-cdef-1234-567890abcdef   5Gi        RWO            fast-storage   15s

Key Concept

If you remember nothing else from this pattern, remember: StorageClasses let Kubernetes create storage automatically when your app asks for it.

Common Mistakes

Not specifying the correct provisioner in the StorageClass.

Kubernetes won't know how to create the storage and the PVC will stay pending.

Use the provisioner that matches your cloud or storage system, like kubernetes.io/aws-ebs for AWS.

Creating a PersistentVolumeClaim without specifying the StorageClass name.

Kubernetes may use the default StorageClass or fail if none is set, causing unexpected storage types or errors.

Always specify the storageClassName field in your PVC to use the desired StorageClass.

Deleting the StorageClass while PVCs are still using it.

Existing volumes may become unmanaged or cause errors when deleted unexpectedly.

Only delete StorageClasses when no PVCs are using them or after cleaning up PVCs.

Summary

Create a StorageClass YAML file to define how storage is dynamically provisioned.

Apply the StorageClass to the cluster using kubectl apply.

Create a PersistentVolumeClaim that requests storage from the StorageClass.

Check the PVC status to confirm storage was provisioned and bound.

Practice

1. What is the main purpose of a StorageClass in Kubernetes?

easy

A. To define how storage volumes are dynamically provisioned

B. To schedule pods on specific nodes

C. To manage network policies

D. To configure container resource limits

Solution

1. Step 1: Understand StorageClass role

   A StorageClass defines parameters for dynamic volume provisioning in Kubernetes.

2. Step 2: Compare with other options

   Scheduling pods, managing network policies, and resource limits are unrelated to StorageClass.

3. Final Answer:

   To define how storage volumes are dynamically provisioned -> Option A

4. Quick Check:

   StorageClass = dynamic provisioning [OK]

Hint: StorageClass controls storage creation, not pods or network [OK]

Common Mistakes:

• Confusing StorageClass with pod scheduling
• Thinking StorageClass manages network policies
• Assuming StorageClass sets container CPU/memory limits

2. Which of the following is the correct YAML snippet to specify a StorageClass named fast-storage for a PersistentVolumeClaim?

easy

A. StorageClass: fast-storage

B. storageclass: fast-storage

C. storageClassName: fast-storage

D. storage_class_name: fast-storage

Solution

1. Step 1: Recall correct field name

   The correct field in PVC spec is storageClassName with camelCase.

2. Step 2: Check other options

   Options B, C, and D use incorrect casing or underscores, which are invalid in Kubernetes YAML.

3. Final Answer:

   storageClassName: fast-storage -> Option C

4. Quick Check:

   Correct YAML key = storageClassName [OK]

Hint: Use exact camelCase 'storageClassName' in PVC spec [OK]

Common Mistakes:

• Using wrong casing like 'storageclass' or 'StorageClass'
• Replacing camelCase with underscores
• Misspelling the field name

3. Given this StorageClass YAML snippet:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: slow
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
reclaimPolicy: Retain

What will happen when a PersistentVolumeClaim requests storage from this class?

medium

A. The volume will not be dynamically provisioned; manual provisioning is required

B. The volume will be deleted automatically when released

C. The volume will be dynamically provisioned immediately

D. The volume will be provisioned but bound immediately without waiting

Solution

1. Step 1: Analyze provisioner field

   The provisioner is kubernetes.io/no-provisioner, meaning no dynamic provisioning.

2. Step 2: Understand reclaimPolicy and binding mode

   ReclaimPolicy is Retain (volume kept after release), and volumeBindingMode waits for pod scheduling.

3. Final Answer:

   The volume will not be dynamically provisioned; manual provisioning is required -> Option A

4. Quick Check:

   No provisioner = manual provisioning [OK]

Hint: No provisioner means no dynamic provisioning [OK]

Common Mistakes:

• Assuming dynamic provisioning happens with no-provisioner
• Confusing reclaimPolicy with provisioning behavior
• Ignoring volumeBindingMode effect

4. You created a StorageClass with volumeBindingMode: Immediate but your pods fail to schedule because volumes are not available in the node's zone. What is the likely cause and fix?

medium

A. Cause: StorageClass name mismatch; Fix: Correct PVC storageClassName

B. Cause: Reclaim policy is Retain; Fix: Change to Delete

C. Cause: Provisioner is missing; Fix: Add a provisioner

D. Cause: Immediate binding ignores pod location; Fix: Change to WaitForFirstConsumer

Solution

1. Step 1: Understand volumeBindingMode impact

   Immediate binding provisions and binds volume before pod scheduling, ignoring node zone.

2. Step 2: Identify fix

   Changing to WaitForFirstConsumer delays binding until pod scheduling, ensuring volume is in correct zone.

3. Final Answer:

   Cause: Immediate binding ignores pod location; Fix: Change to WaitForFirstConsumer -> Option D

4. Quick Check:

   Immediate binding ignores pod zone [OK]

Hint: Use WaitForFirstConsumer to bind volume after pod scheduling [OK]

Common Mistakes:

• Changing reclaimPolicy instead of binding mode
• Adding provisioner when already present
• Fixing storageClassName without checking binding mode

5. You want to create a StorageClass that dynamically provisions SSD-backed volumes with fast performance, deletes volumes when released, and delays binding until pod scheduling. Which YAML snippet correctly implements this?

hard

A. apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: fast-ssd
provisioner: kubernetes.io/aws-ebs
parameters:
type: standard
reclaimPolicy: Retain
volumeBindingMode: Immediate

B. apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: fast-ssd
provisioner: kubernetes.io/aws-ebs
parameters:
type: gp2
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

C. apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: fast-ssd
provisioner: kubernetes.io/no-provisioner
parameters:
type: io1
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

D. apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
name: fast-ssd
provisioner: kubernetes.io/aws-ebs
parameters:
type: io1
reclaimPolicy: Delete
volumeBindingMode: Immediate

Solution

1. Step 1: Identify correct provisioner and parameters

   For AWS SSD, provisioner is kubernetes.io/aws-ebs and type gp2 is general SSD.

2. Step 2: Check reclaimPolicy and binding mode

   ReclaimPolicy should be Delete to remove volumes after release; binding mode WaitForFirstConsumer delays binding until pod scheduling.

3. Step 3: Validate options

   apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: fast-ssd provisioner: kubernetes.io/aws-ebs parameters: type: standard reclaimPolicy: Retain volumeBindingMode: Immediate uses wrong type and policies; apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: fast-ssd provisioner: kubernetes.io/no-provisioner parameters: type: io1 reclaimPolicy: Delete volumeBindingMode: WaitForFirstConsumer uses no provisioner; apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: fast-ssd provisioner: kubernetes.io/aws-ebs parameters: type: io1 reclaimPolicy: Delete volumeBindingMode: Immediate uses Immediate binding which is not desired; apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: fast-ssd provisioner: kubernetes.io/aws-ebs parameters: type: gp2 reclaimPolicy: Delete volumeBindingMode: WaitForFirstConsumer matches all requirements.

4. Final Answer:

   YAML with provisioner kubernetes.io/aws-ebs, type gp2, reclaimPolicy Delete, and WaitForFirstConsumer -> Option B

5. Quick Check:

   Correct provisioner + Delete + WaitForFirstConsumer = apiVersion: storage.k8s.io/v1 kind: StorageClass metadata: name: fast-ssd provisioner: kubernetes.io/aws-ebs parameters: type: gp2 reclaimPolicy: Delete volumeBindingMode: WaitForFirstConsumer [OK]

Hint: Match provisioner, parameters, reclaimPolicy, and bindingMode exactly [OK]

Common Mistakes:

• Using no-provisioner disables dynamic provisioning
• Choosing wrong volume type parameter
• Setting reclaimPolicy to Retain instead of Delete
• Using Immediate binding when delayed binding is needed