KUBERNETES: FROM BASIC TO ADVANCED

Module 3: Configuration & Storage

xdev.asia

🎯 Practice objective__HTMLTAG_68___

• Deploy application with ConfigMaps (env vars and volume mount)
• Create and manage secure Secrets
• Install CSI driver and create StorageClass
• Deploy PostgreSQL with StatefulSet and PersistentVolumeClaim
• Create volume snapshot and perform restore__HTMLTAG_79___

Preparation

kubectl create namespace lab3
kubectl config set-context --current --namespace=lab3

Lab 1: ConfigMaps

# Tạo ConfigMap từ literal values
kubectl create configmap app-config \
  --from-literal=APP_ENV=production \
  --from-literal=APP_PORT=8080 \
  --from-literal=LOG_LEVEL=info \
  -n lab3
Tạo ConfigMap từ file
cat > app.conf <<EOF
[server]
port = 8080
timeout = 30
[database]
host = postgres-service
port = 5432
name = myapp
EOF
kubectl create configmap app-file-config --from-file=app.conf -n lab3
Xem ConfigMap
kubectl get configmaps -n lab3
kubectl describe configmap app-config -n lab3

# Deploy app sử dụng ConfigMap
cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: config-demo
  namespace: lab3
spec:
  replicas: 1
  selector:
    matchLabels:
      app: config-demo
  template:
    metadata:
      labels:
        app: config-demo
    spec:
      containers:
      - name: app
        image: nginx:1.27
        env:
        # Lấy từng key từ ConfigMap
        - name: APP_ENV
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: APP_ENV
        - name: APP_PORT
          valueFrom:
            configMapKeyRef:
              name: app-config
              key: APP_PORT
        # Lấy tất cả keys từ ConfigMap
        envFrom:
        - configMapRef:
            name: app-config
        volumeMounts:
        - name: config-file
          mountPath: /etc/app
      volumes:
      - name: config-file
        configMap:
          name: app-file-config
EOF

# Verify env vars được inject
POD=$(kubectl get pods -n lab3 -l app=config-demo -o jsonpath='{.items[0].metadata.name}')
kubectl exec $POD -n lab3 -- env | grep APP
kubectl exec $POD -n lab3 -- cat /etc/app/app.conf

Lab 2: Secrets

# Tạo Secret
kubectl create secret generic db-credentials \
  --from-literal=POSTGRES_USER=admin \
  --from-literal=POSTGRES_PASSWORD=SuperSecret123 \
  --from-literal=POSTGRES_DB=myapp \
  -n lab3
Secret được lưu dưới dạng base64 (không phải encrypted!)
kubectl get secret db-credentials -n lab3 -o yaml
Decode để xem value
kubectl get secret db-credentials -n lab3 -o jsonpath='{.data.POSTGRES_PASSWORD}' | base64 -d
Deploy app với Secret
cat <<EOF | kubectl apply -f -
apiVersion: apps/v1
kind: Deployment
metadata:
name: postgres-client
namespace: lab3
spec:
replicas: 1
selector:
matchLabels:
app: postgres-client
template:
metadata:
labels:
app: postgres-client
spec:
containers:
- name: app
image: postgres:16
command: ["sleep", "infinity"]
envFrom:
- secretRef:
name: db-credentials
# Mount secret sebagai file
volumeMounts:
- name: secret-volume
mountPath: /etc/secrets
readOnly: true
volumes:
- name: secret-volume
secret:
secretName: db-credentials
EOF
kubectl exec -n lab3 deploy/postgres-client -- env | grep POSTGRES
kubectl exec -n lab3 deploy/postgres-client -- ls /etc/secrets

Lab 3: Immutable ConfigMap and Secret

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: ConfigMap
metadata:
  name: immutable-config
  namespace: lab3
data:
  key1: value1
immutable: true   # không thể update sau khi tạo, chỉ có thể xóa và tạo lại
EOF
Thử update sẽ bị lỗi
kubectl patch configmap immutable-config -n lab3 -p '{"data":{"key1":"new-value"}}'
Error: field is immutable

Lab 4: PersistentVolume and PVC with Local Storage

# Tạo local PV (demo, không dùng production)
cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-pv-1
spec:
  capacity:
    storage: 5Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage
  local:
    path: /tmp/k8s-pv-1
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - kind-worker   # tên node của bạn
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pvc
  namespace: lab3
spec:
  storageClassName: local-storage
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi
EOF
kubectl get pv
kubectl get pvc -n lab3

Lab 5: PostgreSQL with StatefulSet

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: postgres
  namespace: lab3
spec:
  clusterIP: None   # Headless
  selector:
    app: postgres
  ports:
  - port: 5432
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: postgres
  namespace: lab3
spec:
  serviceName: postgres
  replicas: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
      - name: postgres
        image: postgres:16
        ports:
        - containerPort: 5432
        envFrom:
        - secretRef:
            name: db-credentials
        volumeMounts:
        - name: data
          mountPath: /var/lib/postgresql/data
        resources:
          requests:
            cpu: "250m"
            memory: "256Mi"
          limits:
            cpu: "1"
            memory: "512Mi"
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 1Gi
EOF
Theo dõi StatefulSet
kubectl rollout status statefulset/postgres -n lab3
Test connection
kubectl exec -it postgres-0 -n lab3 -- psql -U admin -d myapp -c "CREATE TABLE test (id serial PRIMARY KEY, name text);"
kubectl exec -it postgres-0 -n lab3 -- psql -U admin -d myapp -c "INSERT INTO test (name) VALUES ('hello kubernetes');"
kubectl exec -it postgres-0 -n lab3 -- psql -U admin -d myapp -c "SELECT * FROM test;"

Lab 6: Verify Data Persistence__HTMLTAG_94___

# Xóa pod (StatefulSet sẽ tự tạo lại)
kubectl delete pod postgres-0 -n lab3
Chờ pod mới
kubectl get pods -n lab3 -w
Data vẫn còn sau khi pod restart
kubectl exec -it postgres-0 -n lab3 -- psql -U admin -d myapp -c "SELECT * FROM test;"
Kết quả: "hello kubernetes" vẫn còn

Cleanup

kubectl delete namespace lab3
kubectl delete pv local-pv-1
kubectl config set-context --current --namespace=default

Summary__HTMLTAG_98___

• ✅ ConfigMaps: env vars and volume mount
• ✅ Secrets: save sensitive data (remember: base64, not encrypted)
• ✅ PV/PVC: request and allocate storage__HTMLTAG_105___
• ✅ StatefulSet PostgreSQL: stable identity, persistent storage
• ✅ Data persistence via pod restart__HTMLTAG_109___