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K8s（七）四层代理Service

guduadmin607月前

Service概述

Service在Kubernetes中提供了一种抽象的方式来公开应用程序的网络访问，并提供了负载均衡和服务发现等功能，使得应用程序在集群内外都能够可靠地进行访问。

每个Service都会自动关联一个对应的Endpoint。当创建一个Service时，Kubernetes会根据Service的选择器（selector）来找到匹配的Pod，并将这些Pod的IP地址和端口信息作为Endpoint的一部分。当Service接收到来自外部或内部的请求时，它会将请求转发到与之关联的Endpoint。Endpoint中包含了后端Pod的IP地址和端口信息，Service会根据负载均衡算法将请求转发到一个或多个后端Pod上。并且Service会自动关联到防火墙规则， 将pod的地址和端口保存在防火墙规则内

以上内容由gtp生成

举个例子，以前我访问pod资源要一个一个访问，现在我把一堆具有相同特征（如标签）的pod绑定一个service，然后在service内侧与pod端口绑定，service外侧映射一个端口到宿主机，service还能改dns改防火墙规则。这样直接访问宿主机的端口就能访问到一组pod的特定端口。跟nginx做反向代理负载均衡差不多

#查看帮助
kubectl explain Service
apiVersion   
kind 
metadata     
spec 
status       
kubectl explain Service.spec
allocateLoadBalancerNodePorts  #是否是默认映射端口nodeports
#如果是，则会默认分配到30000-32767随机一个
clusterIP       #service的虚拟ip地址
externalIPs  <[]string> #公开到集群外的ip
externalName  #指定外部dns名称
externalTrafficPolicy  #定义外部流量策略，可选cluster或local
healthCheckNodePort   #用于健康检查的端口
sessionAffinity   #会话策略，可选ClientIP或者None
type   #类型，有四种，ExternalName, ClusterIP, NodePort, LoadBalancer
ports        <[]Object>
kubectl explain service.spec.ports
name 
nodePort      #对外映射的端口
port  -required- #service的端口
protocol      #可选SCTP、TCP、UDP
#在node上下载旧版本的nginx
ctr images pull docker.io/library/nginx:1.21
#创建被管理的pod的yaml文件
#
mkdir service
cd service
cat > pod.yaml << EOF
apiVersion: apps/v1
kind: Deployment
metadata:
  name: pods
spec:
  replicas: 2
  selector:
    matchLabels:
      nginx: "1.21"
  template:
    metadata:
      labels:
        nginx: "1.21"
    spec:
      containers:
        - name: test1
          image: docker.io/library/nginx:1.21
          imagePullPolicy: IfNotPresent
          ports:
            - containerPort: 80
          startupProbe:
            periodSeconds: 5
            initialDelaySeconds: 20
            timeoutSeconds: 5
            httpGet:
              scheme: HTTP
              port: 80
              path: /
          livenessProbe:
            periodSeconds: 5
            initialDelaySeconds: 20
            timeoutSeconds: 5
            httpGet:
              scheme: HTTP
              port: 80
              path: /
          readinessProbe:
            periodSeconds: 5
            initialDelaySeconds: 20
            timeoutSeconds: 5
            httpGet:
              scheme: HTTP
              port: 80
              path: /        
EOF
kubectl apply -f pod.yaml
#成功运行，就不去用curl验证了
kubectl get pods -w
NAME                   READY   STATUS    RESTARTS   AGE
pods-8599b54cf-6tzrx   0/1     Running   0          12s
pods-8599b54cf-vhxd8   0/1     Running   0          12s
pods-8599b54cf-6tzrx   0/1     Running   0          25s
pods-8599b54cf-vhxd8   0/1     Running   0          25s
pods-8599b54cf-6tzrx   1/1     Running   0          25s
pods-8599b54cf-vhxd8   1/1     Running   0          25s
 

ClusterIP模式
 

### ClusterIP模式仅允许集群内部访问
#创建servicea-clusterip.yaml
cat > service-clusterip.yaml << EOF
apiVersion: v1
kind: Service
metadata:
  name: service
spec:
  type: ClusterIP
  ports:
   - port: 80 #service内侧端口
     protocol: TCP
     targetPort: 80 #对应的pod的端口
  selector:    #筛选器，匹配标签nginx="1.21"的pod
     nginx: "1.21"
EOF
kubectl apply -f service.yaml
kubectl get svc
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1                443/TCP   12d
service      ClusterIP   10.107.178.176           80/TCP    31s
#查看Endpoint列表
#只有完成就绪探测的pod才会被service接管，才会被加入endpoint列表中。未完成启动探测的pod也不会
kubectl describe service service | grep Endpoint
Endpoints:         10.10.179.1:80,10.10.234.86:80
kubectl get ep service #也可以
NAME      ENDPOINTS                        AGE
service   10.10.179.1:80,10.10.234.86:80   2m54s
#测试
curl 10.10.179.1:80
#service自动生成域名，仅在pod内可以进行访问
service.default.svc.cluster.local:80
#进入pod
kubectl exec pods-8599b54cf-6tzrx -it -- /bin/sh
curl service.default.svc.cluster.local:80



Welcome to nginx!




Welcome to nginx!


If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.


For online documentation and support please refer to
">nginx.org.

Commercial support is available at
">nginx.com.


Thank you for using nginx.



#清理
kubectl delete -f service-clusterip.yaml

 

nodeport模式
 

#nodeport允许将ServiceIp映射到宿主机外部
#创建service-nodeport.yaml
cat > service-nodeport.yaml << EOF
apiVersion: v1
kind: Service
metadata:
  name: service
spec:
  type: NodePort
  ports:
   - port: 80
     protocol: TCP
     targetPort: 80  #对应的pod的端口
     nodePort: 30080 #映射到物理机的端口，如果不写，会随机分配到30000-32767之间的一个
  selector:          #筛选器，匹配标签nginx="1.21"的pod
     nginx: "1.21"
EOF
kubectl apply -f service-nodeport.yaml
kubectl get svc
NAME         TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP   10.96.0.1              443/TCP        12d
service      NodePort    10.108.9.134           80:30080/TCP   11s
#通过宿主机直接请求如图
ipvsadm -Ln | grep 30080 -A 2
TCP  172.17.0.1:30080 rr
  -> 10.10.179.1:80               Masq    1      0          0
  -> 10.10.234.86:80              Masq    1      0          0
--
TCP  192.168.8.160:30080 rr
  -> 10.10.179.1:80               Masq    1      0          1
  -> 10.10.234.86:80              Masq    1      0          0
--
TCP  192.168.122.1:30080 rr
  -> 10.10.179.1:80               Masq    1      0          0
  -> 10.10.234.86:80              Masq    1      0          0
--
TCP  10.10.189.192:30080 rr
  -> 10.10.179.1:80               Masq    1      0          0
  -> 10.10.234.86:80              Masq    1      0          0
kubectl delete -f service-nodeport.yaml

 

K8s（七）四层代理Service,第1张
 

ExternalName模式
 

充当一个别名，将服务映射到集群外部的一个外部域名。当使用该服务时，Kubernetes会将服务的DNS解析为ExternalName指定的外部域名，从而实现对外部服务的访问。这种模式适用于需要将服务与集群外部的现有服务进行关联的场景。
 

#用以跨namespace调用资源
#创建一个新的ns
kubectl create ns server
#创建server中的yaml文件
cat > pod-in-server.yaml << EOF
apiVersion: apps/v1
kind: Deployment
metadata:
  name: pods
  namespace: server
spec:
  replicas: 2
  selector:
    matchLabels:
      nginx: "1.21"
  template:
    metadata:
      labels:
        nginx: "1.21"
    spec:
      containers:
        - name: test1
          image: docker.io/library/nginx:1.21
          imagePullPolicy: IfNotPresent
EOF
kubectl apply -f pod-in-server.yaml
#创建pod in server中的service四层代理
cat > service-in-server.yaml << EOF
apiVersion: v1
kind: Service
metadata:
  name: service-in-server
  namespace: server
spec:
  selector:
     nginx: "1.21"
  ports:
   - name: http
     protocol: TCP
     port: 80
     targetPort: 80
EOF
kubectl apply -f service-in-server.yaml
#创建default中的service，设置为externalname
cat > service-externalname.yaml << EOF
apiVersion: v1
kind: Service
metadata:
  name: service
spec:
  type: ExternalName
  externalName: service-in-server.server.svc.cluster.local #设置要关联的service的域名
  ports:
   - port: 80
  selector: 
     nginx: "1.21"
EOF
kubectl apply -f service-externalname.yaml
kubectl get pods -n server
NAME                    READY   STATUS    RESTARTS   AGE
pods-8649769f54-fs72b   1/1     Running   0          22s
#进入默认的ns的pod中，通过域名访问server的ns中的pod资源
kubectl exec pods-8599b54cf-6tzrx -it -- /bin/sh
curl service-in-server.server.svc.cluster.local
#可以访问到



Welcome to nginx!




Welcome to nginx!


If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.


For online documentation and support please refer to
">nginx.org.

Commercial support is available at
">nginx.com.


Thank you for using nginx.



#清理
kubectl delete -f service-externalname.yaml
kubectl delete -f service-in-server.yaml
kubectl delete -f pod-in-server.yaml

      
      
	        
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