Kubernetes StatefulSet 学习

Kubernetes-StatefulSet 学习

StatefulSet（有状态集）常用于部署有状态的且需要有序启动的应用程序。StatefulSet主要用于管理有状态应用程序的工作负载API对象。比如在生产环境中，可以部署ElasticSearch集群、MongoDB集群或者需要持久化的RabbitMQ集群、Redis集群、Kafka集群和ZooKeeper集群等。而StatefulSet创建的Pod一般使用Headless Service（无头服务）进行通信。

创建StatefluSet

[root@instance-gvpb80ao yaml]# cat statefluset.yaml
apiVersion: v1
kind: Service
metadata:
 name: nginx
 labels:
   app: nginx
spec:
 ports:
   - port: 80
     name: web
 clusterIP: None
 selector:
   app: nginx
---
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
          ports:
            - containerPort: 80
              name: web
[root@instance-gvpb80ao yaml]# kubectl create -f statefluset.yaml
statefulset.apps/web createdCopy to clipboardErrorCopied

StatefulSet扩容

和Deployment类似，可以通过更新replicas字段扩容/缩容StatefulSet，也可以使用kubectlscale或者kubectlpatch来扩容/缩容一个StatefulSet。

扩容scale

[root@instance-gvpb80ao yaml]# kubectl scale statefulset web --replicas=5
statefulset.apps/web scaled
[root@instance-gvpb80ao yaml]# kubectl get -f statefluset.yaml
NAME            TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
service/nginx   ClusterIP   None         <none>        80/TCP    7m8s

NAME                   READY   AGE
statefulset.apps/web   2/5     3m13sCopy to clipboardErrorCopied

扩容patch

[root@instance-gvpb80ao yaml]# kubectl patch statefulsets.apps web -p '{"spec":{"replicas": 2}}'
statefulset.apps/web patched
[root@instance-gvpb80ao yaml]# kubectl get -f statefluset.yaml
NAME            TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
service/nginx   ClusterIP   None         <none>        80/TCP    8m56s

NAME                   READY   AGE
statefulset.apps/web   4/2     5m1sCopy to clipboardErrorCopied

StatefulSet删除

删除StatefulSet有两种方式，即级联删除和非级联删除。使用非级联方式删除StatefulSet时，StatefulSet的Pod不会被删除；使用级联删除时，StatefulSet和它的Pod都会被删除。

非级联删除

使用kubectl delete sts删除StatefulSet时，只需提供--cascade=false参数，就会采用非级联删除，此时删除StatefulSet不会删除它的Pod。

[root@instance-gvpb80ao yaml]# kubectl delete statefulset web --cascade=false
statefulset.apps "web" deleted
[root@instance-gvpb80ao yaml]# kubectl get pods | grep web
web-0                               1/1     Running            0          13m
web-1                               1/1     Running            0          13mCopy to clipboardErrorCopied

当再次创建此StatefulSet时，web-0会被重新创建，web-1由于已经存在而不会被再次创建，因为最初此StatefulSet的replicas是2，所以web-2会被删除，如下（忽略AlreadyExists错误）

[root@instance-gvpb80ao yaml]# kubectl create -f statefluset.yaml
statefulset.apps/web created
Error from server (AlreadyExists): error when creating "statefluset.yaml": services "nginx" already exists
[root@instance-gvpb80ao yaml]# kubectl get pods | grep web
web-0                               1/1     Running            0          14m
web-1                               1/1     Running            0          14mCopy to clipboardErrorCopied

级联删除

省略--cascade=false参数即为级联删除

[root@instance-gvpb80ao yaml]# kubectl delete -f statefluset.yaml
service "nginx" deleted
statefulset.apps "web" deleted
[root@instance-gvpb80ao yaml]# kubectl get pods | grep web
web-0                               0/1     Terminating        0          16m
web-1                               0/1     Terminating        0          16m

[root@instance-gvpb80ao yaml]# kubectl scale deployment nginx-deployment --replicas=5
deployment.apps/nginx-deployment scaled
[root@instance-gvpb80ao yaml]# kubectl get -f deployment.yaml
NAME               READY   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment   4/5     5            4           31m