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。