apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: db
spec:
  serviceName: db-headless     # 关联的 Headless Service，提供稳定 DNS
  replicas: 3
  selector:
    matchLabels:
      app: db
  template:
    metadata:
      labels:
        app: db
    spec:
      containers:
        - name: db
          image: postgres:16.2
          volumeMounts:
            - name: data
              mountPath: /var/lib/postgresql/data
  volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes: ["ReadWriteOnce"]
        resources:
          requests:
            storage: 20Gi

kubectl get sts db -o wide
kubectl get pods -l app=db -w          # 观察 db-0 → db-1 → db-2 顺序
kubectl scale sts/db --replicas=3