k8s系列---stateful（有状态应用副本集）控制器

http://blog.itpub.net/28916011/viewspace-2215046/

在应用程序中，可以分为有状态应用和无状态应用。

无状态的应用更关注于群体，任何一个成员都可以被取代。

对有状态的应用是关注个体。

像我们前面用deployment控制器管理的nginx、myapp等都属于无状态应用。

像mysql、redis，zookeeper等都属于有状态应用，他们有的还有主从之分、先后顺序之分。

statefulset控制器能实现有状态应用的管理，但实现起来也是非常麻烦的。需要把我们运维管理的过程写入脚本并注入到statefulset中才能使用。虽然互联网上有人做好了stateful的脚本，但是还是建议大家不要轻易的把redis、mysql等这样有状态的应用迁移到k8s上。

在k8s中，statefulset主要管理一下特效的应用：

a)、每一个Pod稳定且有唯一的网络标识符；

b）、稳定且持久的存储设备；

c)、要求有序、平滑的部署和扩展；

d）、要求有序、平滑的终止和删除；

e)、有序的滚动更新，应该先更新从节点，再更新主节点；

statefulset由三个组件组成:

a) headless service（无头的服务，即没名字）；

b）statefulset控制器

c）volumeClaimTemplate（存储卷申请模板，因为每个pod要有专用存储卷，而不能共用存储卷）

[root@master ~]# kubectl explain sts   #stateful的简称

　　

创建之前删除之前创建的多余的pod和svc避免待会冲突出错，当然也可以不删，只不过yaml里有些是冲突的，自己得另行定义

kubectl delete pods pod-vol-pvc
kubectl delete pod pod-cm-3
kubectl delete pods pod-secret-1
kubectl delete deploy myapp-deploy
kubectl delete deploy tomcat-deploy
kubectl delete pvc mypvc
kubectl delete pv --all
kubectl delete svc myapp
kubectl delete svc tomcat

　　

然后重新生成pv

[root@master volumes]# cat pv-demo.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv001
  labels:
    name: pv001
spec:
  nfs:
    path: /data/volumes/v1
    server: 172.16.100.64
  accessModes: ["ReadWriteMany","ReadWriteOnce"]
  capacity:
    storage: 5Gi
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv002
  labels:
    name: pv002
spec:
  nfs:
    path: /data/volumes/v2
    server: 172.16.100.64
  accessModes: ["ReadWriteOnce"]
  capacity:
    storage: 5Gi
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv003
  labels:
    name: pv003
spec:
  nfs:
    path: /data/volumes/v3
    server: 172.16.100.64
  accessModes: ["ReadWriteMany","ReadWriteOnce"]
  capacity:
    storage: 5Gi
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv004
  labels:
    name: pv004
spec:
  nfs:
    path: /data/volumes/v4
    server: 172.16.100.64
  accessModes: ["ReadWriteMany","ReadWriteOnce"]
  capacity:
    storage: 5Gi
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv005
  labels:
    name: pv005
spec:
  nfs:
    path: /data/volumes/v5
    server: 172.16.100.64
  accessModes: ["ReadWriteMany","ReadWriteOnce"]
  capacity:
    storage: 9Gi

　　

[root@master stateful]# cat stateful-demo.yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp-svc
  labels:
    app: myapp-svc
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None
  selector:
    app: myapp-pod
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: myapp
spec:
  serviceName: myapp-svc
  replicas: 2
  selector:
    matchLabels:
      app: myapp-pod
  template:
    metadata:
      labels:
        app: myapp-pod
    spec:
      containers:
      - name: myapp
        image: ikubernetes/myapp:v1
        ports:
        - containerPort: 80
          name: web
        volumeMounts:
        - name: myappdata
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates: #存储卷申请模板，可以为每个pod定义volume；可以为pod所在的名称空间自动创建pvc。
  - metadata:
      name: myappdata
    spec:
      accessModes: ["ReadWriteOnce"]
      #storageClassName: "gluster-dynamic"
      resources:
        requests:
          storage: 5Gi #2G的pvc

　　

[root@master stateful]# kubectl apply -f stateful-demo.yaml
service/myapp-svc unchanged
statefulset.apps/myapp created

　　

[root@master stateful]# kubectl get svc
NAME         TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)             AGE
myapp-svc    ClusterIP   None            <none>        80/TCP              12m

　　

看到myapp-svc是无头服务。

[root@master stateful]# kubectl get sts
NAME      DESIRED   CURRENT   AGE
myapp     2         2         6m

　　

[root@master stateful]# kubectl get pvc
NAME                STATUS    VOLUME    CAPACITY   ACCESS MODES   STORAGECLASS   AGE
myappdata-myapp-0   Bound     pv002     2Gi        RWO                           3s
myappdata-myapp-1   Bound     pv003     1Gi        RWO,RWX                       1s

　　

[root@master stateful]# kubectl get pv
NAME      CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM                       STORAGECLASS   REASON    AGE
pv001     1Gi        RWO,RWX        Retain           Available                                                        1d
pv002     2Gi        RWO            Retain           Bound       default/myappdata-myapp-0                            1d
pv003     1Gi        RWO,RWX        Retain           Bound       default/myappdata-myapp-1                            1d
pv004     1Gi        RWO,RWX        Retain           Bound       default/mypvc                                        1d
pv005     1Gi        RWO,RWX        Retain           Available

　　

[root@master stateful]# kubectl get pods
NAME                             READY     STATUS             RESTARTS   AGE
myapp-0                          1/1       Running            0          4m
myapp-1                          1/1       Running            0          4m

　　

[root@master stateful]# kubectl delete -f stateful-demo.yaml
service "myapp-svc" deleted
statefulset.apps "myapp" deleted

　　

上面删除会使pod和service删除，但是pvc是不会删除，所以还能恢复。

[root@master stateful]# kubectl exec -it myapp-0 -- /bin/sh
/ # nslookup myapp-0.myapp-svc.default.svc.cluster.local
nslookup: can't resolve '(null)': Name does not resolve
Name:      myapp-0.myapp-svc.default.svc.cluster.local
Address 1: 10.244.1.110 myapp-0.myapp-svc.default.svc.cluster.local
/ #
/ #
/ # nslookup myapp-1.myapp-svc.default.svc.cluster.local
nslookup: can't resolve '(null)': Name does not resolve
Name:      myapp-1.myapp-svc.default.svc.cluster.local
Address 1: 10.244.2.97 myapp-1.myapp-svc.default.svc.cluster.local

　　

myapp-0.myapp-svc.default.svc.cluster.local

格式为:pod_name.service_name.namespace.svc.cluster.local

下面扩展myapp pod为5个：

[root@master stateful]# kubectl scale sts myapp --replicas=5
statefulset.apps/myapp scaled

　　

[root@master stateful]# kubectl get pods
NAME                             READY     STATUS             RESTARTS   AGE
client                           0/1       Error              0          17d
myapp-0                          1/1       Running            0          37m
myapp-1                          1/1       Running            0          37m
myapp-2                          1/1       Running            0          46s
myapp-3                          1/1       Running            0          43s
myapp-4                          0/1       Pending            0          41s

　　

[root@master stateful]# kubectl get pvc
NAME                STATUS    VOLUME    CAPACITY   ACCESS MODES   STORAGECLASS   AGE
myappdata-myapp-0   Bound     pv002     2Gi        RWO                           52m
myappdata-myapp-1   Bound     pv003     1Gi        RWO,RWX                       52m
myappdata-myapp-2   Bound     pv005     1Gi        RWO,RWX                       2m
myappdata-myapp-3   Bound     pv001     1Gi        RWO,RWX                       2m
myappdata-myapp-4   Pending                                                      2m

　　

另外也可以用patch打补丁的方法来进行扩容和缩容：

[root@master stateful]# kubectl patch sts myapp -p '{"spec":{"replicas":2}}'
statefulset.apps/myapp patched

　　

下面我们再来介绍一下滚动更新。

[root@master stateful]# kubectl explain sts.spec.updateStrategy.rollingUpdate

　　

假设有4个pod（pod0,pod1,pod2,pod3），如果设置partition为5，那么说明大于等于5的pod更新，我们四个Pod就都不更新；如果partition为4，那么说明大于等于4的pod更新，即pod3更新，其他pod都不更新；如果partiton为3，那么说明大于等于3的pod更新，那么就是pod2和pod3更新，其他pod都不更新。

[root@master stateful]# kubectl patch sts myapp -p '{"spec":{"updateStrategy":{"rollingUpdate":{"partition":4}}}}'
statefulset.apps/myapp patched

　　

1.13和视频中partition是不一样，视频版本1.11？？出现的是4，1.13.怎么该也不是4显示的是一大串数字。，但是更新是按照上面的策略更新的

[root@master stateful]# kubectl describe sts myapp
Update Strategy:    RollingUpdate
Partition:        4

　　

下面把myapp升级为v2版本

[root@master stateful]# kubectl set image sts/myapp myapp=ikubernetes/myapp:v2
statefulset.apps/myapp image updated
[root@master ~]# kubectl get sts -o wide
NAME      DESIRED   CURRENT   AGE       CONTAINERS   IMAGES
myapp     2         2         1h        myapp        ikubernetes/myapp:v2
[root@master ~]# kubectl get pods myapp-4 -o yaml
 containerStatuses:
  - containerID: docker://898714f2e5bf4f642e2a908e7da67eebf6d3074c89bbd0d798d191a2061a3115
    image: ikubernetes/myapp:v2

　　

可以看到pod myapp-4使用的模板版本是v2了。