Kubernetes (K8s) StatefulSet (sts)

Greetings of the day dear Orchestrator!! In this post, we will discuss exploring the Kubernetes StatefulSet(sts) 

What is the purpose of Stateful deployment?

Kubernetes' basic unit is Pod, which will be ephemeral in nature and it was designed in such a way that it cannot store the state. To store and maintain the state of the application, Kubernetes introduced a new type of deployment manifestation called it as StatefulSet.

Here in this post, we will be experimenting with the most important deployment model that is StatefulSet which will be interconnected with the multiple storage related objects PersistantVolume(PV) and PersistentVolumeClaim (PVC).   

Assumptions

To work on this experiment you must have Kubernetes cluster running on single node or multi-node and it should have a NFS remote storage access that depends on your platform. Here I've EC2 instance having  NFS service configured and run:

• Kubernetes Cluster configured and Up
• Prepare a NFS server up and running on EC2 centos instance

Let's define the couple of PV(4) using the NFS server which will be consumed by the PVC. The Stateful deployment is going to have the Pod and PVC template manifestation.

Creating a YAML file for pvc :

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv0
spec:
  storageClassName: manual
  capacity:
    storage: 200Mi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /export/volume/pv0
    server: 172.31.46.253
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv1
spec:
  storageClassName: manual
  capacity:
    storage: 200Mi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /export/volume/pv1
    server: 172.31.46.253
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv2
spec:
  storageClassName: manual
  capacity:
    storage: 200Mi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /export/volume/pv2
    server: 172.31.46.253
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv3
spec:
  storageClassName: manual
  capacity:
    storage: 200Mi
  volumeMode: Filesystem
  accessModes:
    - ReadWriteOnce
  mountOptions:
    - hard
    - nfsvers=4.1
  nfs:
    path: /export/volume/pv3
    server: 172.31.46.253

Now, use the following command to create the PVC:

Syntax :
kubectl create -f nfs-pv.yaml

Output :



Checking the PVC are created or not with the simple ls command :

Syntax :

ls

Output :

Using another YAML file for creating PV files :

---
apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web-sts
spec:
  serviceName: "nginx"
  replicas: 4
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: gcr.io/google_containers/nginx-slim:0.8
        ports:
        - containerPort: 80
          name: web-sts
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      storageClassName: manual
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 100Mi 

Now, use the following command to create the PV:

Syntax:

kubectl create -f web-sts.yaml

Output :

Checking the PV are created or not with the following command :

Syntax :

kubectl get pv 

Output :

Ready to use Statefulsets now, you can watch all the running terms at one place by using the below command :
Syntax :

watch kubectl get all

Output :