Merge pull request devopsproin#4 from devopsproin/statefulset

Statefulset

StatefulSet/README.md

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+# Kubernetes StatefulSet Guide
+## Headless Service
+The Headless Service YAML file defines a Kubernetes Service that does not assign an IP address to the pods. It is used for discovering and connecting to individual pods directly.
+
+service.yaml:
+```
+apiVersion: v1
+kind: Service
+metadata:
+  name: headless-svc
+spec:
+  selector:
+    app: nginx
+  ports:
+  - port: 80
+    name: web
+  clusterIP: None
+```
+
+### To apply the Headless Service YAML file, use the following command:
+```
+kubectl apply -f service.yaml
+```
+
+### To retrieve the information about the "headless-svc" service, use the following command:
+```
+kubectl get service headless-svc
+```
+
+## StatefulSet
+The StatefulSet YAML file defines a Kubernetes StatefulSet, which manages the deployment and scaling of stateful applications. In this example, it creates and manages two replicas of an nginx application.
+
+sts.yaml:
+```
+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: web
+spec:
+  serviceName: "headless-svc"
+  replicas: 2
+  selector:
+    matchLabels:
+      app: nginx
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: registry.k8s.io/nginx-slim:0.8
+        ports:
+        - containerPort: 80
+          name: web
+```
+
+### To apply the StatefulSet YAML file, use the following command:
+```
+kubectl apply -f sts.yaml
+```
+
+### To retrieve the information about the "web" StatefulSet, including the number of replicas and their current status, use the following command:
+```
+kubectl get sts web
+```
+
+### To retrieve the information about the pods associated with the "nginx" application and continuously monitors their status, use the following command:
+```
+kubectl get pods -w -l app=nginx
+```
+
+### To scale the "web" StatefulSet, use the following command:
+```
+kubectl scale sts web --replicas=4
+```
+
+### To delete the "web" StatefulSet and all associated pods, use the following command:
+```
+kubectl delete sts web
+```
+
+## Storage with StatefulSet
+The Storage with StatefulSet YAML file extends the previous StatefulSet example by adding a PersistentVolumeClaim (PVC) for storage using volumeClaimTemplates field. It mounts a volume to the nginx containers in the StatefulSet.
+
+sts.yaml:-
+```
+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: web
+spec:
+  serviceName: "headless-svc"
+  replicas: 2
+  selector:
+    matchLabels:
+      app: nginx
+  template:
+    metadata:
+      labels:
+        app: nginx
+    spec:
+      containers:
+      - name: nginx
+        image: registry.k8s.io/nginx-slim:0.8
+        ports:
+        - containerPort: 80
+          name: web
+        volumeMounts:
+        - name: web-pvc
+          mountPath: /usr/share/nginx/html
+  volumeClaimTemplates:
+  - metadata:
+      name: web-pvc
+    spec:
+      accessModes: [ "ReadWriteOnce" ]
+      resources:
+       
+```
+
+### To apply the Storage with StatefulSet YAML file to create the StatefulSet with persistent storage in the Kubernetes cluster, use the following command:
+```
+kubectl apply -f sts.yaml
+```
+
+In conclusion, this Kubernetes StatefulSet Guide provides a set of YAML files and commands to help you deploy and manage stateful applications in a Kubernetes cluster. It covers the creation of a Headless Service for direct pod discovery and connection, the deployment and scaling of a StatefulSet with replicas, and the integration of persistent storage using a PersistentVolumeClaim (PVC). By following the instructions and using the provided examples, you can effectively utilize StatefulSets and leverage the power of Kubernetes for your stateful application needs.