Kubernetes Storage Solutions: Volumes and Persistent Storage

Introduction

As the Chief Architect with extensive experience in cloud computing and strategic IT architectures, I have consistently explored the intricacies of Kubernetes and its pivotal role in modern application deployment and management. Kubernetes, an open-source system for automating deployment, scaling, and management of containerized applications, has revolutionized the way we handle cloud applications. A critical aspect of this system is its storage solutions, particularly volumes and persistent storage. In this article, we’ll delve into real-world use-cases, complete with YAML snippets, to illustrate the practicality and versatility of Kubernetes storage solutions.

Use-Case 1: Simple Volume in a Pod

One of the simplest use-cases involves deploying a pod with a Kubernetes volume. This example demonstrates a pod definition with an emptyDir volume.

apiVersion: v1
kind: Pod
metadata:
  name: simple-pod
spec:
  containers:
  - name: web-container
    image: nginx
    volumeMounts:
    - mountPath: /cache
      name: cache-volume
  volumes:
  - name: cache-volume
    emptyDir: {}

Here, an emptyDir volume is created and mounted at /cache in the Nginx container. This is useful for temporary data that lives as long as the pod lives.

Use-Case 2: Persistent Volume (PV) and Persistent Volume Claim (PVC)

In more complex scenarios, persistent storage is required. Kubernetes Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) offer a solution for long-term storage needs. Below is an example of a PersistentVolume and a PersistentVolumeClaim.

PersistentVolume:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-volume
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  hostPath:
    path: /data/pv-volume

PersistentVolumeClaim:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pv-claim
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 3Gi

This pair allows a user to request storage resources without knowing the details of the underlying storage infrastructure.

After setting up a Persistent Volume (PV) and a Persistent Volume Claim (PVC), the next step is to use the PVC in a pod. This integration is crucial for applications that need persistent data across pod restarts or deployments. Below is an example of how to incorporate a PVC into a pod configuration.

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  containers:
    - name: myfrontend
      image: nginx
      volumeMounts:
      - mountPath: "/var/www/html"
        name: mypd
  volumes:
    - name: mypd
      persistentVolumeClaim:
        claimName: pv-claim

In this YAML snippet, a pod named mypod is defined with a single container running Nginx. The key part is the volumeMounts section. Here, the volume named mypd is mounted inside the container at the path /var/www/html. This volume is tied to the PVC named pv-claim, which we defined earlier.

This setup ensures that the data stored in /var/www/html inside the Nginx container is persisted across pod restarts, making it ideal for applications that require long-term data retention, such as web applications, database applications or file storage systems.

Use-Case 3: Dynamic Provisioning with StorageClass

Dynamic provisioning is a feature that automatically creates storage resources. It’s achieved using the StorageClass resource.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gp2
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
reclaimPolicy: Retain
allowVolumeExpansion: true

This YAML creates a StorageClass named ‘gp2’ that provisions AWS EBS volumes. By referencing this StorageClass in a PVC, Kubernetes dynamically provisions the necessary PV.

Conclusion

Kubernetes storage solutions, including volumes, PVs, PVCs, and dynamic provisioning with StorageClasses, offer robust and flexible options for managing application data. The examples provided here are just a glimpse into the potential and versatility of Kubernetes storage. By understanding and utilizing these concepts, developers and architects can significantly enhance the efficiency and reliability of their Kubernetes applications.

About the Author

Rajesh Gheware is a seasoned Chief Architect with over 23 years of experience in cloud computing, IoT, software development, and strategic IT architectures. With significant roles at UniGPS Solutions, JP Morgan Chase, and Deutsche Bank Group, and an M.Tech from IIT Madras, Rajesh brings a wealth of knowledge and expertise to the field. He is also active in technical communities, contributing to platforms like DZone, GitHub.