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K8s学习笔记——StatefulSet之拓扑状态

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学习极客时间上的《深入剖析Kubernetes》

秉持眼过千遍不如手过一遍的原则。动手实践并记录结果

对应章节：18 | 深入理解StatefulSet（一）：拓扑状态

Headless Service

创建service

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apiVersion: v1
kind: Service
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: nginx
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$ kubectl get service
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
nginx        ClusterIP   None         <none>        80/TCP    129m

创建StatefulSet

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apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 80
          name: web
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$ kubectl apply -f statefulset.yaml
statefulset.apps/web created
$ kubectl get pods -w -l app=nginx
NAME    READY   STATUS              RESTARTS   AGE
web-0   1/1     Running             0          2s
web-1   0/1     ContainerCreating   0          1s
web-1   1/1     Running             0          2s
$ kubectl get statefulset -o wide
NAME   READY   AGE   CONTAINERS   IMAGES
web    2/2     52s   nginx        nginx
$ kubectl get pods -o wide
NAME    READY   STATUS    RESTARTS   AGE   IP            NODE            NOMINATED NODE   READINESS GATES
web-0   1/1     Running   0          85s   172.1.1.199   node2           <none>           <none>
web-1   1/1     Running   0          81s   172.1.2.180   bqi-k8s-node3   <none>           <none>

可以看出，statefulset创建出来的pod，名字是固定的，而不再像deployment中的，pod名字会变化

验证

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$ kubectl exec web-0 -- sh -c 'hostname'
web-0
$ kubectl exec web-1 -- sh -c 'hostname'
web-1
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$ kubectl run -i --tty --image busybox:1.28.4 web-test --restart=Never --rm -- /bin/sh
If you don't see a command prompt, try pressing enter.
/ # nslookup web-0.nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-0.nginx
Address 1: 172.1.1.199 web-0.nginx.default.svc.cluster.local
/ # nslookup web-1.nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-1.nginx
Address 1: 172.1.2.180 web-1.nginx.default.svc.cluster.local
/ #

重建pod

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$ kubectl delete pod -l app=nginx
pod "web-0" deleted
pod "web-1" deleted
# 快速执行
$ kubectl get pod -w -l app=nginx
NAME    READY   STATUS              RESTARTS   AGE
web-0   0/1     ContainerCreating   0          0s
web-0   1/1     Running             0          1s
web-1   0/1     Pending             0          0s
web-1   0/1     Pending             0          0s
web-1   0/1     ContainerCreating   0          0s
web-1   1/1     Running             0          3s
$  kubectl get pods -o wide
NAME    READY   STATUS    RESTARTS   AGE   IP            NODE            NOMINATED NODE   READINESS GATES
web-0   1/1     Running   0          85s   172.1.1.201   node2           <none>           <none>
web-1   1/1     Running   0          81s   172.1.2.181   bqi-k8s-node3   <none>           <none>

可以看到，当删除了相关的pod后，kubernetes会以同样的名字重建pod

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$ kubectl run -i --tty --image busybox:1.28.4 connect-test --restart=Never --rm -- /bin/sh
If you don't see a command prompt, try pressing enter.
/ # nslookup web-0.nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-0.nginx
Address 1: 172.1.1.201 web-0.nginx.default.svc.cluster.local
/ # nslookup web-1.nginx
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      web-1.nginx
Address 1: 172.1.2.181 web-1.nginx.default.svc.cluster.local
/ #

重建后，依然可以访问web-0.nginx，但IP地址发生了变化

小结

本节课程主要学习了StatefulSet这个控制器，K8s在按照pod模版进行创建时：

  1. 对pod进行编号并逐一完成创建工作
  2. 当重建发生时，也会按照编号对pod逐一进行操作
  3. 通过headless service，StatefulSet 为每个 Pod 创建了一个固定并且稳定的 DNS 记录
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