k8s系列---stateful（有狀態應用副本集）控制器

時間 2019-12-08

標籤 k8s 系列 stateful 狀態應用副本控制器简体版

原文原文鏈接

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

在應用程序中，能夠分爲有狀態應用和無狀態應用。 python

無狀態的應用更關注於羣體，任何一個成員均可以被取代。 mysql

對有狀態的應用是關注個體。 nginx

像咱們前面用deployment控制器管理的nginx、myapp等都屬於無狀態應用。 web

像mysql、redis，zookeeper等都屬於有狀態應用，他們有的還有主從之分、前後順序之分。 redis

statefulset控制器能實現有狀態應用的管理，但實現起來也是很是麻煩的。須要把咱們運維管理的過程寫入腳本並注入到statefulset中才能使用。雖然互聯網上有人作好了stateful的腳本，可是仍是建議你們不要輕易的把redis、mysql等這樣有狀態的應用遷移到k8s上。sql

在k8s中，statefulset主要管理一下特效的應用： docker

a)、每個Pod穩定且有惟一的網絡標識符；api

b）、穩定且持久的存儲設備； tomcat

c)、要求有序、平滑的部署和擴展；

d）、要求有序、平滑的終止和刪除；

e)、有序的滾動更新，應該先更新從節點，再更新主節點；

statefulset由三個組件組成:

a) headless service（無頭的服務，即沒名字）；

b）statefulset控制器

c）volumeClaimTemplate（存儲卷申請模板，由於每一個pod要有專用存儲卷，而不能共用存儲卷）

[root@master ~]# kubectl explain sts   #stateful的簡稱

建立以前刪除以前建立的多餘的pod和svc避免待會衝突出錯，固然也能夠不刪，只不過yaml裏有些是衝突的，本身得另行定義

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

而後從新生成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: #存儲卷申請模板，能夠爲每一個pod定義volume；能夠爲pod所在的名稱空間自動建立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是無頭服務。

[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

上面刪除會使pod和service刪除，可是pvc是不會刪除，因此還能恢復。

[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

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

下面擴展myapp pod爲5個：

[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

另外也能夠用patch打補丁的方法來進行擴容和縮容：

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

下面咱們再來介紹一下滾動更新。

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

假設有4個pod（pod0,pod1,pod2,pod3），若是設置partition爲5，那麼說明大於等於5的pod更新，咱們四個Pod就都不更新；若是partition爲4，那麼說明大於等於4的pod更新，即pod3更新，其餘pod都不更新；若是partiton爲3，那麼說明大於等於3的pod更新，那麼就是pod2和pod3更新，其餘pod都不更新。

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

1.13和視頻中partition是不同，視頻版本1.11？？出現的是4，1.13.怎麼該也不是4顯示的是一大串數字。，可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升級爲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

能夠看到pod myapp-4使用的模板版本是v2了。