# StatefulSet：部署有状态的多副本应用

很高兴大家能做到这里，这是容器kubernetes内容最后一个章节了！而且非常简单，恭喜大家！

## 部署有状态的集群应用

针对有状态的应用，多数是数据有状态，例如mongodb副本集等，我们希望数据能够在pod扩容、缩容时磁盘数据不会被丢弃，能够复用磁盘。我们使用StatefulSet完成这些。

```yaml
# cat kubia-statefulset.yaml
apiVersion: apps/v1
kind: StatefulSet         #使用了stateful
metadata: 
  name: kubia
spec:
  serviceName: kubia
  replicas: 2
  selector:
    matchLabels:
     app: kubia
  template:
    metadata:
      labels:
        app: kubia
    spec:
      containers:
      - name: kubia
        image: luksa/kubia-pet
        ports:
        - name: http
          containerPort: 8080
        volumeMounts:
        - name: data
          mountPath: /var/data
  volumeClaimTemplates:   #为每个pod申请了磁盘  
  - metadata:
      name: data
    spec:
      resources:
        requests:
          storage: 20Gi
      accessModes:
      - ReadWriteOnce
      storageClassName: "alicloud-disk-available"
```

创建它看看，大家能够注意到，每个pod名字不再是随机码了，而是有了编号，他们也就是有了固定的名字了，所以对应的磁盘也是有了名字

```yaml
$ k create -f kubia-statefulset.yaml
statefulset.apps/kubia created

$ k get all
NAME          READY   STATUS    RESTARTS   AGE
pod/kubia-0   1/1     Running   0          61s
pod/kubia-1   1/1     Running   0          46s

NAME                     READY   AGE
statefulset.apps/kubia   2/2     61s

$ k get pvc
NAME           STATUS   VOLUME                   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
data-kubia-0   Bound    d-j6c3dilgxismppu271ed   20Gi       RWO            disk           7m39s
data-kubia-1   Bound    d-j6c9x6t7z31woktn8jl3   20Gi       RWO            disk           7m24s
```

这样他们在随着容量变化时，总是能够对号入座，是不是很简单呢？另外StatefulSet相比ReplicaSet，操作基本都是相同的，所以扩缩容等管理我们就不重复了

```yaml
# 如
$ kubectl scale statefulset kubia --replicas=3                                                                                                                                 1 ↵
statefulset.apps/kubia scaled
```

{% hint style="success" %}
StatefulSet在缩容时，pod卸下的磁盘不会被清理掉，因为扩容时还会再被复用，这是固定的机制。大家要记得这个点。
{% endhint %}

Cool！其实StatefulSet是很简单的，但是很多服务都会用到它，需要多练习。

好了，课程到这里告一段落，再次恭喜大家完成了这么多的内容。

## 思考题

> * 谈谈你对ReplicaSet/StatefulSet的理解
> * Deployment和上面两个set有关联么，谈谈你的理解
> * 谈谈你对kubernetes的体验感受


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://doc.spotmaxtech.com/she-qu-huo-dong/kubernetes-workshop/additional/statefulset-bu-shu-you-zhuang-tai-de-duo-fu-ben-ying-yong.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.