Kubernetes运维之容器编排StatefulSet

[root@k8s-master1 ~]# kubectl explain sts.spec
KIND:     StatefulSet
VERSION:  apps/v1

RESOURCE: spec <Object>

DESCRIPTION:
     Spec defines the desired identities of pods in this set.

     A StatefulSetSpec is the specification of a StatefulSet.

FIELDS:
   podManagementPolicy  <string>  # POD启动规则，OrderedReady有序启动，Parallel一起启动
     podManagementPolicy controls how pods are created during initial scale up,
     when replacing pods on nodes, or when scaling down. The default policy is
     `OrderedReady`, where pods are created in increasing order (pod-0, then
     pod-1, etc) and the controller will wait until each pod is ready before
     continuing. When scaling down, the pods are removed in the opposite order.
     The alternative policy is `Parallel` which will create pods in parallel to
     match the desired scale without waiting, and on scale down will delete all
     pods at once.

   replicas     <integer> # 副本数量
     replicas is the desired number of replicas of the given Template. These are
     replicas in the sense that they are instantiations of the same Template,
     but individual replicas also have a consistent identity. If unspecified,
     defaults to 1.

   revisionHistoryLimit <integer> # 保留历史副本
     revisionHistoryLimit is the maximum number of revisions that will be
     maintained in the StatefulSet's revision history. The revision history
     consists of all revisions not represented by a currently applied
     StatefulSetSpec version. The default value is 10.

   selector     <Object> -required- # labels标签
     selector is a label query over pods that should match the replica count. It
     must match the pod template's labels. More info:
     https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/#label-selectors

   serviceName  <string> -required-  # service网络访问名称
     serviceName is the name of the service that governs this StatefulSet. This
     service must exist before the StatefulSet, and is responsible for the
     network identity of the set. Pods get DNS/hostnames that follow the
     pattern: pod-specific-string.serviceName.default.svc.cluster.local where
     "pod-specific-string" is managed by the StatefulSet controller.

   template     <Object> -required-  # POD模板
     template is the object that describes the pod that will be created if
     insufficient replicas are detected. Each pod stamped out by the StatefulSet
     will fulfill this Template, but have a unique identity from the rest of the
     StatefulSet.

   updateStrategy       <Object> # 滚动更新规则
     rollingUpdate:
       partition: 2  <integer> # 只会更新大于等于这个索引的POD

   volumeClaimTemplates <[]Object>  # 挂载数据信息
     volumeClaimTemplates is a list of claims that pods are allowed to
     reference. The StatefulSet controller is responsible for mapping network
     identities to claims in a way that maintains the identity of a pod. Every
     claim in this list must have at least one matching (by name) volumeMount in
     one container in the template. A claim in this list takes precedence over
     any volumes in the template, with the same name.

---
apiVersion: v1
kind: Service
metadata:
  name: nginx   # 与下面serviceName相同
  labels:
    app: nginx
spec:
  ports:
  - port: 80
    name: web
  clusterIP: None  ## 不分配ClusterIP，代表headless service网络，整个集群的Pod能访问，外部不能访问
  selector:
    app: nginx
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx"
  replicas: 3
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: web
#        volumeMounts:
#        - name: www
#          mountPath: /usr/share/nginx/html
#  volumeClaimTemplates:
#  - metadata:
#      name: www
#      annotations:
#        volume.alpha.kubernetes.io/storage-class: anything
#    spec:
#      accessModes: [ "ReadWriteOnce" ]
#      resources:
#        requests:
#          storage: 1Gi

[root@k8s-master1 ~]# kubectl get pod                       
NAME    READY   STATUS              RESTARTS   AGE
web-0   1/1     Running             0          72s
web-1   1/1     Running             0          43s
web-2   0/1     ContainerCreating   0          3s
[root@k8s-master1 ~]# kubectl get pod
NAME    READY   STATUS    RESTARTS   AGE
web-0   1/1     Running   0          2m22s
web-1   1/1     Running   0          113s
web-2   1/1     Running   0          73s

# 查看创建的headless service和statefulset
[root@k8s-master1 ~]# kubectl get s
secrets                        serviceaccounts                services                       statefulsets.apps              storageclasses.storage.k8s.io
[root@k8s-master1 ~]# kubectl get statefulsets.apps 
NAME   READY   AGE
web    3/3     3m13s
[root@k8s-master1 ~]# kubectl get statefulsets
NAME   READY   AGE
web    3/3     3m16s
# 其他pod中访问
root@nginx-deployment-594d59fb8d-56nfd:/# curl web-0.nginx
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>

# 扩容
$ kubectl scale statefulset web --replicas=5

# 缩容
$ kubectl patch statefulset web -p '{"spec":{"replicas":3}}'

# 镜像更新（目前还不支持直接更新image，需要patch来间接实现）
$ kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"gcr.io/google_containers/nginx-slim:0.7"}]'

# 删除StatefulSet和Headless Service
$ kubectl delete statefulset web
$ kubectl delete service nginx

# StatefulSet删除后PVC还会保留着，数据不再使用的话也需要删除
$ kubectl delete pvc www-web-0 www-web-1