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Storage in Kubernetes

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Dhanush Gowda
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5 min read

1. Understanding Key Concepts

Persistent Volumes (PV)

  • A Persistent Volume (PV) is a piece of storage in the Kubernetes cluster that has been provisioned either statically or dynamically. It is a cluster-wide resource that abstracts the underlying physical storage and is managed by Kubernetes.

  • PVs are independent of the lifecycle of any individual Pod that uses the volume. This means they can be reused and are not tied to any specific Pod.

Persistent Volume Claim (PVC)

  • A Persistent Volume Claim (PVC) is a request for storage by a user. It specifies the amount of storage and the access modes (read/write) required.

  • PVCs are bound to a PV that meets the request. The Kubernetes scheduler automatically selects the PV that satisfies the claim and binds them together.

StorageClass

  • A StorageClass defines the type of storage to be used and how it should be provisioned.

    • It can specify things like the provisioner (which cloud provider, or storage system), volume type (e.g., SSD, HDD), replication, performance tiers (e.g., Standard, Premium), and other parameters.

    • When PVCs are created, they reference a StorageClass that defines how the underlying volume is provisioned and what kind of performance/storage options are available.

2. Static Provisioning

Static provisioning means that Persistent Volumes (PVs) are pre-created manually by administrators. Users can then request the available PVs by creating Persistent Volume Claims (PVCs).

Static Provisioning in Azure (AKS)

Storage Options for Static Provisioning in Azure (AKS):

  1. Azure Managed Disks
    Azure Managed Disks are the default disk storage solution. They are scalable and high-performance.

    • Use Case: Used for applications that require high-performance block-level storage.

    • Types: Standard HDD, Standard SSD, Premium SSD.

  2. Azure Files
    Azure Files is a fully managed file share service in the cloud, accessible using the SMB (Server Message Block) protocol.

    • Use Case: Used for shared file storage where multiple clients may need access, such as for lifting and shifting legacy apps or shared storage.

Steps for Static Provisioning in AKS:

  1. Create the Azure Disk/Files:

    • Azure disks are created manually through Azure Portal, CLI, or ARM templates.

    • For Azure Files, create a file share in the Azure Storage account.

  2. Create a Persistent Volume (PV):

    • You need to manually define the PV in Kubernetes by specifying the disk or file share URL.

  3. Create Persistent Volume Claim (PVC):

    • After PV creation, users can create PVCs that will bind to the manually created PV.

Example PV for Azure Disk:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: azure-disk-pv
spec:
  capacity:
    storage: 10Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  azureDisk:
    diskName: <disk-name>
    diskURI: <disk-uri>
    kind: Managed
    fsType: ext4

PVC Example:

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

Static Provisioning in AWS (EKS)

Storage Options for Static Provisioning in AWS (EKS):

  1. Amazon EBS (Elastic Block Store)

    • EBS is a scalable and persistent block-level storage service.

    • Use Case: Used for high-performance applications, databases, or for scenarios where direct block storage is required.

  2. Amazon EFS (Elastic File System)

    • Amazon EFS is a scalable and managed file storage system for use with AWS Cloud services and on-premises resources.

    • Use Case: Shared access to file-based storage across multiple instances.

Steps for Static Provisioning in EKS:

  1. Create the EBS Volume or EFS:

    • EBS volumes are created manually via AWS Console or CLI.

    • EFS filesystems are also created through the AWS Console/CLI and mounted to EC2 instances.

  2. Create Persistent Volume (PV):

    • Manually create the PV and reference the EBS volume or EFS filesystem.

  3. Create Persistent Volume Claim (PVC):

    • After creating the PV, users can create PVCs to claim the manually created PVs.

Example PV for EBS Volume:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: ebs-pv
spec:
  capacity:
    storage: 10Gi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  awsElasticBlockStore:
    volumeID: <volume-id>
    fsType: ext4

PVC Example:

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

3. Dynamic Provisioning

Dynamic provisioning refers to Kubernetes automatically provisioning storage for a PVC based on a StorageClass definition. This eliminates the need to manually create PVs.

Dynamic Provisioning in Azure (AKS)

Storage Options for Dynamic Provisioning in Azure (AKS):

  1. Azure Managed Disks (Premium SSD, Standard SSD, Standard HDD)
    Azure Disks can be dynamically provisioned based on the StorageClass parameters you specify.

  2. Azure Files
    Azure Files can also be dynamically provisioned using the right StorageClass.

Steps for Dynamic Provisioning in AKS:

  1. Create a StorageClass: Define the type of Azure Disk (e.g., Premium SSD).

  2. Create a PVC: When a PVC is created, Kubernetes will automatically provision the storage.

Example StorageClass for Dynamic Provisioning:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: azure-disk
provisioner: kubernetes.io/azure-disk
parameters:
  storageaccounttype: Premium_LRS

PVC Example:

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

When this PVC is created, Kubernetes will automatically provision an Azure Disk using the azure-disk StorageClass.

Dynamic Provisioning in AWS (EKS)

Storage Options for Dynamic Provisioning in AWS (EKS):

  1. Amazon EBS (Elastic Block Store)

    • EBS can be dynamically provisioned using the AWS EBS CSI driver.

  2. Amazon EFS (Elastic File System)

    • EFS can also be dynamically provisioned using the AWS EFS CSI driver.

Steps for Dynamic Provisioning in EKS:

  1. Install the CSI Drivers: Install the EBS CSI driver or EFS CSI driver on your EKS cluster.

  2. Create a StorageClass: Define the storage options for dynamic provisioning.

  3. Create a PVC: When a PVC is created, Kubernetes will automatically provision the volume based on the StorageClass.

Example for EBS CSI Driver and StorageClass:

StorageClass for EBS:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-sc
provisioner: ebs.csi.aws.com
parameters:
  type: gp2

PVC Example:

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

When this PVC is created, Kubernetes will automatically provision an EBS volume using the ebs-sc StorageClass.

Key Takeaways

  • PV (Persistent Volume): A cluster-wide storage resource provisioned statically or dynamically.

  • PVC (Persistent Volume Claim): A user’s request for storage, which can be dynamically bound to a PV.

  • StorageClass: Defines the provisioning type (dynamic or static) and other parameters for storage like disk type, replication, etc.

  • Static Provisioning: PVs are created manually and then bound to PVCs. Common for managing storage options like Azure Disks, EBS, or NFS.

  • Dynamic Provisioning: PVs are automatically created by Kubernetes when a PVC is created. It uses StorageClasses to define how volumes are provisioned,

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