statefulSet 为每一个pod提供一个稳定的、唯一的网络标识符，每个 Pod 通过 PersistentVolumeClaim (PVC) 获得自己的存储。即使 Pod 被重新调度到另一个节点，这个 PVC 也会被重新挂载到正确的 Pod 上，保证存储的稳定性。

statefulset创建的pod是有序的，比如statefulset叫web，那么创建的两个pods叫做web_0 web_1. web_0删掉以后，新创建的还叫web_0

新创建的statefulset必须要标记serviceName，这个name将是pod的名称前缀

[root@master stateful]# cat statefulset.yaml 
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector: 
    matchLabels:
      app: nginx
  serviceName: "nginx"
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
          name: web
---
apiVersion: v1
kind: Service
metadata: 
  name: nginx
  labels:
    app: nginx
spec:
 ports:
 - port: 80
   name: web
 clusterIP: None
 selector:
   app: nginx

注意上面的service没有cluster IP

[root@master stateful]# kubectl get pods -owide
NAME                               READY   STATUS    RESTARTS   AGE     IP               NODE    NOMINATED NODE   READINESS GATES
nfs-provisioner-5654cf4975-sqfpv   1/1     Running   0          166m    10.244.166.129   node1   <none>           <none>
web-0                              1/1     Running   0          5m43s   10.244.166.141   node1   <none>           <none>
web-1                              1/1     Running   0          5m41s   10.244.104.37    node2   <none>           <none>
[root@master stateful]# kubectl delete pods web-1
pod "web-1" deleted
[root@master stateful]# kubectl get pods -owide
NAME                               READY   STATUS              RESTARTS   AGE     IP               NODE    NOMINATED NODE   READINESS GATES
nfs-provisioner-5654cf4975-sqfpv   1/1     Running             0          167m    10.244.166.129   node1   <none>           <none>
web-0                              1/1     Running             0          6m16s   10.244.166.141   node1   <none>           <none>
web-1                              0/1     ContainerCreating   0          2s      <none>           node2   <none>           <none>

可以看到删除web_1后，会重新创建一个新的（ip不一样）

然后通过nslookup解析服务nginx，由于没有clusterIP，会直接解析到两个pod的地址

直接解析web_0的名称，也可以直接解析到pod地址

[root@master storage_test]# kubectl run busybox --image=docker.io/library/busybox:1.28 --image-pull-policy=IfNotPresent --restart=Never --rm -it 

If you don't see a command prompt, try pressing enter.

/ # nslookup nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      nginx
Address 1: 10.244.104.38 web-1.nginx.default.svc.cluster.local
Address 2: 10.244.166.141 web-0.nginx.default.svc.cluster.local
/ # nslookup web-0.nginx.default.svc.cluster.local
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-0.nginx.default.svc.cluster.local
Address 1: 10.244.166.141 web-0.nginx.default.svc.cluster.local
/ # exit