Mastering Persistent Storage in Kubernetes StatefulSets with Amazon EBS on EKS

Introduction to Kubernetes Storage Concepts and Amazon EBS Integration

Kubernetes, the leading container orchestration platform, is built to manage large-scale containerized applications. A key aspect of managing these applications is ensuring that data persists beyond the lifecycle of individual containers. In Kubernetes, persistent storage is critical for stateful applications, where the state needs to be retained across pod restarts and rescheduling.

Amazon Elastic Block Store (EBS) is a highly available and scalable block storage service designed for use with Amazon EC2. It seamlessly integrates with Kubernetes, particularly on Amazon Elastic Kubernetes Service (EKS), to provide persistent storage for Kubernetes workloads. With Amazon EBS, Kubernetes can dynamically provision volumes to persist data generated by stateful applications.

Understanding Container Storage Interface (CSI) and Its Role in EKS

The Container Storage Interface (CSI) is a standard designed to abstract the complexities of storage management in containerized environments. It enables Kubernetes to integrate with different storage systems without depending on specific APIs. This abstraction is crucial for providing consistent storage management across various Kubernetes clusters.

In Amazon EKS, the EBS CSI driver manages the lifecycle of Amazon EBS volumes. It allows for dynamic provisioning of EBS volumes, attachment to Kubernetes pods, and managing the volumes’ lifecycle. This integration simplifies using EBS volumes in a Kubernetes environment, ensuring that stateful workloads have reliable, persistent storage.

Installing the EBS CSI Driver for Dynamic Volume Provisioning

To leverage Amazon EBS volumes in Kubernetes, you must install the EBS CSI driver on your EKS cluster. The installation involves deploying the driver as a Kubernetes DaemonSet, ensuring it runs on all nodes within the cluster.

Here’s how you can install the EBS CSI driver:

Add the EBS CSI Driver Helm repository:
helm repo add aws-ebs-csi-driver https://kubernetes-sigs.github.io/aws-ebs-csi-driver

helm repo update

Install the driver using Helm:
helm install aws-ebs-csi-driver aws-ebs-csi-driver/aws-ebs-csi-driver \

–namespace kube-system \

–set image.repository=602401143452.dkr.ecr.us-west-2.amazonaws.com/eks/aws-ebs-csi-driver \

–set controller.serviceAccount.create=true \

–set controller.serviceAccount.name=ebs-csi-controller-sa

This installation enables dynamic volume provisioning, automatically enabling Kubernetes to create and manage EBS volumes as needed.

Deploying StatefulSets with Amazon EBS Volumes for Persistent Storage

StatefulSets in Kubernetes are designed for stateful applications, where each pod needs persistent storage. By integrating Amazon EBS volumes with StatefulSets, you ensure that each pod in the StatefulSet has its persistent storage that survives restarts and rescheduling.

Here’s an example YAML configuration for a StatefulSet using EBS volumes:

apiVersion: apps/v1

kind: StatefulSet

metadata:

spec:

serviceName: “nginx”

replicas: 3

selector:

matchLabels:

app: nginx

template:

metadata:

labels:

app: nginx

spec:

containers:

– name: nginx

image: k8s.gcr.io/nginx-slim:0.8

ports:

– containerPort: 80

volumeMounts:

– name: web-data

mountPath: /usr/share/nginx/html

volumeClaimTemplates:

– metadata:

spec:

accessModes: [ “ReadWriteOnce” ]

storageClassName: “gp2”

resources:

requests:

storage: 1Gi

In this example, each replica of the NGINX StatefulSet gets its EBS-backed volume, ensuring that the data stored by each replica persists across pod restarts.

Demonstrating Persistent Storage with EBS Volumes in StatefulSets

Once you have deployed your StatefulSet, you can test the persistence of data by performing the following steps:

Create a file in one of the StatefulSet pods:
kubectl exec -it web-0 — /bin/bash

echo “Persistent Data” > /usr/share/nginx/html/index.html

exit

Delete the pod:
kubectl delete pod web-0
Verify that the data persists:
After the pod is rescheduled, verify that the data is still available:
kubectl exec -it web-0 — cat /usr/share/nginx/html/index.html

The content “Persistent Data” should still be present, demonstrating that the EBS volume has persisted the data across the pod lifecycle.

Comparing Ephemeral and Persistent Volumes in Kubernetes

Kubernetes supports both temporary and persistent storage. Ephemeral storage is temporary and tied to a pod’s lifecycle, meaning data is lost when a pod is deleted or rescheduled. This is suitable for stateless applications or when data persistence is not critical.

Persistent storage, on the other hand, is independent of the pod lifecycle. Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) manage persistent storage, which survives pod restarts, rescheduling, and even cluster upgrades. Amazon EBS volumes are an example of persistent storage in Kubernetes, providing a reliable solution for stateful applications.

Practical Exercises: Testing Ephemeral and Persistent Storage in StatefulSets

To gain hands-on experience with transient and persistent storage in Kubernetes, try the following exercises:

Deploy a StatefulSet with temporary storage and observe the data loss upon pod deletion and rescheduling.
Deploy a StatefulSet with persistent storage using Amazon EBS volumes and verify data persistence across the pod lifecycle.
Switch a StatefulSet from ephemeral to persistent storage and observe how data retention improves.

These exercises will help you understand the critical differences between transient and persistent storage and the scenarios where each is applicable.