有状态应用和无状态应用区别

• 无状态应用

Node1故障,在Node2上自动拉起可以继续提供服务,即为无状态应用

应用场景: Nginx, 微服务,jar

• 有状态应用

Node1故障,在Node2上自动拉起不可以继续提供服务,即为有状态应用

应用场景: Mysql主从,zookeeper集群,etcd集群

需要考虑问题:

1. 数据持久化
2. IP地址
3. 启动顺序

在k8s中,有状态应用一般指的是分布式应用程序

StatefulSet控制器概述

• 部署有状态应用

• 解决Pod独立生命周期，保持Pod启动顺序和唯一性

1. 稳定，唯一的网络标识符，持久存储

2. 有序，优雅的部署和扩展、删除和终止

3. 有序，滚动更新

应用场景：分布式应用

稳定的网络ID

• headless Service

标准service (normal service)

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: nginx 
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

无头service (headless service)

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  clusterIP: None
  selector:
    app: nginx 
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

示例: StatefulSet控制器+headless service

apiVersion: v1
kind: Service
metadata:
  name: nginx-headless
spec:
  clusterIP: None
  selector:
    app: nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

---

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: nginx-sts
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx-headless"
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: http

验证

kubectl get svc
kubectl get ep

# 解析验证
kubectl run -it --image busybox:1.28.4 --rm dns-test  /bin/sh

# nslookup nginx-headless
Server:    10.0.0.10
Address 1: 10.0.0.10

Name:      nginx-headless
Address 1: 10.244.1.51
Address 2: 10.244.2.95

访问地址

# 解析格式
<pod_name>.<service_name>.<ns_name>.svc.cluster.local
# 例如:
ping nginx-sts-1.nginx-headless.default.svc.cluster.local
PING nginx-sts-1.nginx-headless.default.svc.cluster.local (10.244.1.51): 56 data bytes
64 bytes from 10.244.1.51: seq=0 ttl=62 time=0.613 ms
64 bytes from 10.244.1.51: seq=1 ttl=62 time=0.329 ms
64 bytes from 10.244.1.51: seq=2 ttl=62 time=0.293 ms

稳定的存储

apiVersion: v1
kind: Service
metadata:
  name: nginx-headless
spec:
  clusterIP: None
  selector:
    app: nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

---

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: nginx-sts
spec:
  selector:
    matchLabels:
      app: nginx
  serviceName: "nginx-headless"
  replicas: 2
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
          name: http
          
        volumeMounts:
        - name: pvc-www03
          mountPath: /usr/share/nginx/html
          
          
  volumeClaimTemplates:
  - metadata:
      name: pvc-www03
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "managed-nfs-storage"
      resources:
        requests:
          storage: 1Gi

验证:

kubectl get pvc
kubectl get pv

查看NFS共享目录,分别为两个pod各自创建了一个存储目录, 也就是说每个pod的数据存储是独立的

其中一个pod的数据目录创建一个文件1.txt,然后删除此pod,等待pod自动拉起,查看数据目录的数据是否存在,如果存在,表示pod已经持久化存储