Lab15 Complete

k8s/STATEFULSET.md

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+# StatefulSet Overview
+
+**StatefulSet Use Cases:**
+- Databases (MySQL, PostgreSQL, MongoDB)
+- Message queues (Kafka, RabbitMQ)
+- Distributed systems (Elasticsearch, Cassandra)
+
+**Key Differences:**
+
+| Feature | Deployment | StatefulSet |
+|---------|------------|-------------|
+| Pod Names | Random suffix | Ordered index (pod-0, pod-1) |
+| Storage | Shared PVC | Per-pod PVC via templates |
+| Scaling | Any order | Ordered (0→1→2) |
+| Network ID | Random | Stable DNS name |
+
+**Headless Service:**
+A Service with `clusterIP: None` creates DNS records for each pod:
+- `pod-0.service-name.namespace.svc.cluster.local`
+
+# Resource Verification
+
+```bash
+kubectl get statefulset
+```
+```text
+NAME         READY   AGE
+dinfochart   5/5     3m23s
+```
+```bash
+kubectl get pods
+```
+```text
+NAME           READY   STATUS    RESTARTS   AGE
+dinfochart-0   1/1     Running   0          3m31s
+dinfochart-1   1/1     Running   0          3m23s
+dinfochart-2   1/1     Running   0          3m17s
+dinfochart-3   1/1     Running   0          3m11s
+dinfochart-4   1/1     Running   0          3m6s
+```
+```bash
+kubectl get pvc
+```
+```text
+NAME                           STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   VOLUMEATTRIBUTESCLASS   AGE
+data-dinfochart-0              Bound    pvc-784ff82c-411e-4a10-b051-7c83c2cb4b97   100Mi      RWO            standard       <unset>                 10m
+dinfochart-data                Bound    pvc-70bb3538-0219-4095-b89d-9b660b8e7b57   100Mi      RWO            standard       <unset>                 3m38s
+dinfochart-data-dinfochart-0   Bound    pvc-e23d9b83-fdfa-4aee-a16b-0d9c88f3b280   100Mi      RWO            standard       <unset>                 3m38s
+dinfochart-data-dinfochart-1   Bound    pvc-567e3999-61c7-4296-b1ba-55cdcb738833   100Mi      RWO            standard       <unset>                 3m30s
+dinfochart-data-dinfochart-2   Bound    pvc-b8897836-6f0e-4f1d-96bc-550579591d6d   100Mi      RWO            standard       <unset>                 3m24s
+dinfochart-data-dinfochart-3   Bound    pvc-3c88cd06-04e5-4fbb-8099-779ab5523c84   100Mi      RWO            standard       <unset>                 3m18s
+dinfochart-data-dinfochart-4   Bound    pvc-1d982389-ea92-4957-9e2d-450462809574   100Mi      RWO            standard       <unset>                 3m13s
+```
+
+# Network Identity
+
+```text
+/app # nslookup dinfochart-1.dinfochart-headless.default.svc.cluster.loc
+al
+Server:         10.96.0.10
+Address:        10.96.0.10:53
+
+
+Name:   dinfochart-1.dinfochart-headless.default.svc.cluster.local
+Address: 10.244.0.10
+```
+
+# Per-Pod Storage Evidence
+```text
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ curl localhost:8080/vis
+its
+Handling connection for 8080
+{"visits":1}
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ curl localhost:8081/vis
+its
+Handling connection for 8081
+{"visits":4}
+```
+
+# Persistence Test
+```
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ kubectl exec dinfochart
+-0 -- cat /data/visits && echo
+1
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ kubectl delete pod dinf
+ochart-0
+pod "dinfochart-0" deleted from default namespace
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ kubectl get pods
+NAME           READY   STATUS    RESTARTS   AGE
+dinfochart-0   1/1     Running   0          10s
+dinfochart-1   1/1     Running   0          20m
+dinfochart-2   1/1     Running   0          19m
+dinfochart-3   1/1     Running   0          19m
+dinfochart-4   1/1     Running   0          19m
+timur@timur-ficus:~/proj/DevOps-Core-Course/k8s$ kubectl exec dinfochart
+-0 -- cat /data/visits && echo
+1
+```

k8s/dinfochart/templates/headless-service.yaml

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+apiVersion: v1
+kind: Service
+metadata:
+  name: {{ include "dinfochart.fullname" . }}-headless
+spec:
+  clusterIP: None
+  selector:
+    {{- include "dinfochart.selectorLabels" . | nindent 4 }}
+  ports:
+    - port: {{ .Values.service.port }}

k8s/dinfochart/templates/statefulset.yaml

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+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: {{ include "dinfochart.fullname" . }}
+spec:
+  serviceName: {{ include "dinfochart.fullname" . }}-headless
+  replicas: {{ .Values.replicaCount }}
+  selector:
+    matchLabels:
+      {{- include "dinfochart.selectorLabels" . | nindent 6 }}
+  template:
+    metadata:
+      labels:
+        {{- include "dinfochart.labels" . | nindent 8 }}
+        {{- with .Values.podLabels }}
+        {{- toYaml . | nindent 8 }}
+        {{- end }}
+      annotations:
+        vault.hashicorp.com/agent-inject: "true"
+        vault.hashicorp.com/role: "dinfoservice-role"
+        vault.hashicorp.com/agent-inject-secret-config: "secret/data/myapp/config"
+    spec:
+      containers:
+        - name: {{ .Chart.Name }}
+          image:  "{{ .Values.image.repository }}:{{ .Values.image.tag | default .Chart.AppVersion }}"
+          ports:
+          - containerPort: {{ .Values.service.port }}
+          {{- with .Values.resources }}
+          resources:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
+          {{- with .Values.livenessProbe }}
+          livenessProbe:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
+          {{- with .Values.readinessProbe }}
+          readinessProbe:
+            {{- toYaml . | nindent 12 }}
+          {{- end }}
+          volumeMounts:
+            - name: app-config
+              mountPath: /config
+              readOnly: true
+            - name: data-volume
+              mountPath: /data
+          envFrom:
+            - configMapRef:
+                name: {{ include "dinfochart.fullname" . }}-env
+      volumes:
+        - name: app-config
+          configMap:
+            name: {{ include "dinfochart.fullname" . }}-config
+        - name: data-volume
+          persistentVolumeClaim:
+            claimName: {{ include "dinfochart.fullname" . }}-data
+  volumeClaimTemplates:
+    - metadata:
+        name: {{ include "dinfochart.fullname" . }}-data
+      spec:
+        accessModes: [ "ReadWriteOnce" ]
+        resources:
+          requests:
+            storage: {{ .Values.persistence.size }}