1. StatefulSet 简介#

StatefulSet 是 Kubernetes 中用于 有状态应用（Stateful Applications）的控制器，与 Deployment 类似，但提供稳定的 Pod 标识、持久存储和有序部署等特性。常用于 数据库、分布式存储、ZooKeeper、Kafka 等应用。

StatefulSet 主要特点：

1. 稳定的网络标识（Pod 名称唯一且有序）。
2. 稳定且持久的存储（每个 Pod 绑定独立的 PV，不随 Pod 删除）。
3. 有序部署、扩容、缩容、删除（保证 Pod 按序号启动/停止）。
4. 支持拓扑感知（不同 Pod 可部署到不同节点）。

2. StatefulSet 关键组件#

3. StatefulSet 拓扑结构#

StatefulSet 主要通过 Headless Service 结合 DNS 解析，确保每个 Pod 都有稳定的 FQDN：

+--------------------+
| Service: my-svc   |
| ClusterIP: None   |  <---  通过 DNS 解析 Pod
+--------------------+
          |
 ------------------------
 |        |        |
Pod-0   Pod-1   Pod-2

• Pod 名称固定，例如 web-0, web-1, web-2
• 解析方式：web-0.my-svc.default.svc.cluster.local
• 允许应用使用 直接 Pod-to-Pod 连接，适用于数据库主从复制等场景。

4. StatefulSet 存储管理#

在 StatefulSet 中，每个 Pod 绑定一个 独立的 PersistentVolume (PV)，即使 Pod 重新调度，也会保持相同的存储数据。

+----------------------+     +----------------------+
| Pod-0 (web-0)       | --> | PVC-0 -> PV-0       |
+----------------------+     +----------------------+
| Pod-1 (web-1)       | --> | PVC-1 -> PV-1       |
+----------------------+     +----------------------+

📌 重要特性：

1. PVC 绑定不变：Pod-0 永远绑定 PVC-0，不会与 Pod-1 共享。
2. 适用于数据库、分布式存储，保证数据持久化，不会因 Pod 重新调度丢失。

5. StatefulSet 部署示例#

apiVersion: v1
kind: Service
metadata:
  name: my-svc
spec:
  clusterIP: None   # Headless Service
  selector:
    app: my-app
  ports:
    - port: 80

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "my-svc"
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
        volumeMounts:
        - name: web-storage
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: web-storage
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi

6. StatefulSet 关键特性#

7. StatefulSet 拓扑调度#

（1）节点亲和性（Node Affinity） 指定 Pod 只能运行在 region=us-east-1 的节点：

    affinity:
      nodeAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          nodeSelectorTerms:
          - matchExpressions:
            - key: topology.kubernetes.io/region
              operator: In
              values:
              - us-east-1

（2）Pod 反亲和性（Pod Anti-Affinity） 确保 Pod 不运行在相同节点，提高可用性：

    affinity:
      podAntiAffinity:
        requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: app
                operator: In
                values:
                - my-app
            topologyKey: "kubernetes.io/hostname"

8. StatefulSet 操作#

kubectl get statefulset
kubectl describe statefulset web

kubectl get pods -o wide
kubectl get pvc
kubectl get pv

kubectl exec -it web-0 -- /bin/sh

kubectl scale statefulset web --replicas=5

kubectl delete statefulset web --cascade=orphan  # 保留 PVC

9. StatefulSet VS Deployment#

练习, MySQL StatefulSet的部署：

1. Headless Service:

apiVersion: v1
kind: Service
metadata:
  name: mysql
spec:
  clusterIP: None
  selector:
    app: mysql
  ports:
  - name: mysql
    port: 3306

(base) PS C:\Users\Kevin Leen\OneDrive - San Jose-Evergreen Community College District\Desktop\k8s> k get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
kubernetes   ClusterIP   172.20.0.1   <none>        443/TCP    67m
mysql        ClusterIP   None         <none>        3306/TCP   10s

(base) PS C:\Users\Kevin Leen\OneDrive - San Jose-Evergreen Community College District\Desktop\k8s> k get ep
NAME         ENDPOINTS                       AGE
kubernetes   10.0.2.177:443,10.0.3.135:443   69m
mysql        <none>                          2m20s

2. PVC:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: gp2 # 明确指定使用 gp2 StorageClass
  resources:
    requests:
      storage: 10Gi

EKS中的storageclass :

kubectl get storageclass
NAME            PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
gp2 (default)   kubernetes.io/aws-ebs   Delete          WaitForFirstConsumer   false                  61m

(base) PS C:\Users\Kevin Leen\OneDrive - San Jose-Evergreen Community College District\Desktop\k8s> k get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)    AGE
kubernetes   ClusterIP   172.20.0.1   <none>        443/TCP    68m
mysql        ClusterIP   None         <none>        3306/TCP   96s

3. StatefulSet

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
spec:
  serviceName: "mysql"
  replicas: 1 
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
	initContainers:
	- name: data-cleanup
	  image: busybox:1.28
	  command: ["sh", "-c", "rm -rf /var/lib/mysql/*"] #提前清理数据避免报错
	  volumeMounts:
		- name: mysql-persistent-storage
		  mountPath: /var/lib/mysql
      containers:
      - name: mysql
        image: mysql:5.7 
        ports:
        - containerPort: 3306
        env:
        - name: MYSQL_ROOT_PASSWORD
          value: "your_root_password" 
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pvc

(base) PS C:\Users\Kevin Leen\OneDrive - San Jose-Evergreen Community College District\Desktop\k8s> k exec -it mysql-0 -c mysql -- sh
sh-4.2#             
sh-4.2# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.44 MySQL Community Server (GPL)

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