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k8s之Service详解-Service使用


实验环境准备

 在使用service之前,首先利用deployment创建出3个pod,注意要为pod设置app=nginx-pod的标签

创建deployment.yaml,内容如下

apiVersion: apps/v1 kind: Deployment metadata:    name: pc-deployment   namespace: dev spec:   replicas: 3   selector:     matchLabels:       app: nginx-pod   template:     metadata:        labels:         app: nginx-pod     spec:       containers:       - name: nginx         image: nginx:1.17.1         ports:          - containerPort: 80

使用配置文件

[root@master ~]# vim deployment.yaml [root@master ~]# kubectl create -f deployment.yaml  deployment.apps/pc-deployment created [root@master ~]# kubectl get pod -n dev -o wide NAME                             READY   STATUS    RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES pc-deployment-6696798b78-5d7rh   1/1     Running   0          4s    10.244.2.4    node2   <none>           <none> pc-deployment-6696798b78-5jbcr   1/1     Running   0          4s    10.244.1.26   node1   <none>           <none> pc-deployment-6696798b78-wbrfh   1/1     Running   0          4s    10.244.2.3    node2   <none>           <none>

通过pod的Ip加上容器端口80访问nginx,发现可以访问

[root@master ~]# curl 10.244.2.4:80 <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title>

为了方便后面的测试,修改下面三台nginx的index.html页面(三台修改的Ip地址不一致)

#修改第一个pod [root@master ~]# kubectl exec -it pc-deployment-6696798b78-5d7rh -n dev /bin/sh # echo "10.244.2.4" > /usr/share/nginx/html/index.html # exit  #测试访问 [root@master ~]# curl 10.244.2.4:80 10.244.2.4  #修改第二个pod [root@master ~]# kubectl exec -it pc-deployment-6696798b78-5jbcr -n dev /bin/sh # echo "10.244.1.26" > /usr/share/nginx/html/index.html # exit  #修改第三个pod [root@master ~]# kubectl exec -it pc-deployment-6696798b78-wbrfh -n dev /bin/sh # echo "10.244.2.3" > /usr/share/nginx/html/index.html # exit

ClusterIp类型的Service

创建service-clusterip.yaml文件

apiVersion: v1 kind: Service metadata:   name: service-clusterip   namespace: dev spec:   selector:     app: nginx-pod   clusterIP: 10.97.97.97  #service的Ip地址,如果不写,会默认生成一个   type: ClusterIP   ports:   - port: 80  #service端口     targetPort: 80  #pod端口

 使用配置文件

[root@master ~]# vim service-clusterip.yaml [root@master ~]# kubectl create -f service-clusterip.yaml  service/service-clusterip created [root@master ~]# kubectl get svc service-clusterip -n dev NAME                TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE service-clusterip   ClusterIP   10.97.97.97   <none>        80/TCP    44s  #查看service详细信息 [root@master ~]# kubectl describe svc service-clusterip -n dev Name:              service-clusterip Namespace:         dev Labels:            <none> Annotations:       <none> Selector:          app=nginx-pod Type:              ClusterIP IP:                10.97.97.97 Port:              <unset>  80/TCP TargetPort:        80/TCP Endpoints:         10.244.1.26:80,10.244.2.3:80,10.244.2.4:80 Session Affinity:  None Events:            <none>  #查看ipvs映射规则 [root@master ~]# ipvsadm -Ln IP Virtual Server version 1.2.1 (size=4096) Prot LocalAddress:Port Scheduler Flags   -> RemoteAddress:Port           Forward Weight ActiveConn InActConn TCP  10.97.97.97:80 rr   -> 10.244.1.27:80               Masq    1      0          0            -> 10.244.2.5:80                Masq    1      0          0            -> 10.244.2.6:80                Masq    1      0          0  

EndPoint

Endpoint是k8s中的一个资源对象,存储在etcd中,用来记录一个service对应的所有pod的访问地址,它是根据service配置文件中的selector描述产生的

一个service由一组pod组成,这些pod通过endpoints暴露出来,endpoints是实现实际服务的端点集合。换句话说,service和pod之间的联系是通过endpoints实现的。

k8s之Service详解-Service使用

[root@master ~]# kubectl get endpoints -n dev -o wide NAME                ENDPOINTS                                    AGE service-clusterip   10.244.1.26:80,10.244.2.3:80,10.244.2.4:80   18m

负载分发策略

对service的访问被分发到了后端的pod上去,目前k8s提供了两种负载分发策略:

  • 如果不定义,默认使用kube-proxy的策略,比如随机,轮询
  • 基于客户端地址的会话保持模式,即来自同一个客户端发起的所有请求都会转发到一个固定的pod上,此模式可以使在spec中添加sessionAffinity:ClientIP选项
#查看ipvs映射规则 [root@master ~]# ipvsadm -Ln IP Virtual Server version 1.2.1 (size=4096) Prot LocalAddress:Port Scheduler Flags   -> RemoteAddress:Port           Forward Weight ActiveConn InActConn TCP  10.97.97.97:80 rr   -> 10.244.1.27:80               Masq    1      0          0            -> 10.244.2.5:80                Masq    1      0          0            -> 10.244.2.6:80                Masq    1      0          0    #循环访问测试 [root@master ~]# while true;do curl 10.97.97.97:80;sleep 5;done; 10.244.1.26 10.244.2.3 10.244.2.4 10.244.1.26 10.244.2.3 10.244.2.4 10.244.1.26 10.244.2.3 10.244.2.4

修改分发策略为sessionAffinity:ClientIP

#删除原来的service [root@master ~]# kubectl delete -f service-clusterip.yaml  service "service-clusterip" deleted  #更改service-clusterip.yaml [root@master ~]# vim service-clusterip.yaml  apiVersion: v1 kind: Service metadata:   name: service-clusterip   namespace: dev spec:   sessionAffinity: ClientIP   selector:     app: nginx-pod   clusterIP: 10.97.97.97  #service的Ip地址,如果不写,会默认生成一个   type: ClusterIP   ports:   - port: 80  #service端口     targetPort: 80  #pod端口  #重建service [root@master ~]# kubectl create -f service-clusterip.yaml service/service-clusterip created  #查看svc,可以发现新增了一项SessionAffinity [root@master ~]# kubectl describe svc service-clusterip -n dev Name: service-clusterip Namespace: dev Labels: <none> Annotations: <none> Selector: app=nginx-pod Type: ClusterIP IP: 10.97.97.97 Port: <unset> 80/TCP TargetPort: 80/TCP Endpoints: 10.244.1.27:80,10.244.2.5:80,10.244.2.6:80 Session Affinity: ClientIP Events: <none>

重新查看ipvs映射规则【persistent代表持久】,发现新增了persistent 10800秒,代表持续180分钟

[root@master ~]# ipvsadm -Ln IP Virtual Server version 1.2.1 (size=4096) Prot LocalAddress:Port Scheduler Flags   -> RemoteAddress:Port           Forward Weight ActiveConn InActConn TCP  10.97.97.97:80 rr persistent 10800   -> 10.244.1.27:80               Masq    1      0          0            -> 10.244.2.5:80                Masq    1      0          0            -> 10.244.2.6:80                Masq    1      0          0  

再次进行循环访问测试,发现这次只访问一个pod

[root@master ~]# while true;do curl 10.97.97.97:80;sleep 5;done; 10.244.2.4 10.244.2.4 10.244.2.4 10.244.2.4 10.244.2.4 10.244.2.4

HeadLiness类型的Service

在某些场景中,开发人员可能不想使用Service提供的负载均衡功能,而希望自己来控制负载均衡策略,针对这种情况,k8s提供了HeadLiness Service,这类Service不会分配ClusterIP,如果想要访问Service,只能通过service的域名进行查询。

创建service-headliness.yaml

apiVersion: v1 kind: Service metadata:   name: service-headliness   namespace: dev spec:   selector:     app: nginx-pod   clusterIP: None  #将clusterIP设置为None,即可创建headliness Service   type: ClusterIP   ports:   - port: 80     targetPort: 80

使用配置文件

[root@master ~]# vim service-headliness.yaml [root@master ~]# kubectl create -f service-headliness.yaml  service/service-headliness created [root@master ~]# kubectl get svc service-headliness -n dev NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE service-headliness   ClusterIP   None         <none>        80/TCP    31s [root@master ~]# kubectl describe svc service-headliness -n dev Name: service-headliness Namespace: dev Labels: <none> Annotations: <none> Selector: app=nginx-pod Type: ClusterIP IP: None Port: <unset> 80/TCP TargetPort: 80/TCP Endpoints: 10.244.1.27:80,10.244.2.5:80,10.244.2.6:80 Session Affinity: None Events: <none>

查看域名解析情况

[root@master ~]# kubectl exec -it pc-deployment-6696798b78-5d7rh -n dev /bin/sh # cat /etc/resolv.conf nameserver 10.96.0.10 search dev.svc.cluster.local svc.cluster.local cluster.local options ndots:5 # exit  #通过域名进行查询 [root@master ~]# dig @10.96.0.10 service-headliness.dev.svc.cluster.local  ; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.5 <<>> @10.96.0.10 service-headliness.dev.svc.cluster.local ; (1 server found) ;; global options: +cmd ;; Got answer: ;; WARNING: .local is reserved for Multicast DNS ;; You are currently testing what happens when an mDNS query is leaked to DNS ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40115 ;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1 ;; WARNING: recursion requested but not available  ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;service-headliness.dev.svc.cluster.local. IN A  ;; ANSWER SECTION: service-headliness.dev.svc.cluster.local. 30 IN    A 10.244.2.6 service-headliness.dev.svc.cluster.local. 30 IN    A 10.244.1.27 service-headliness.dev.svc.cluster.local. 30 IN    A 10.244.2.5  ;; Query time: 334 msec ;; SERVER: 10.96.0.10#53(10.96.0.10) ;; WHEN: 四 8月 12 11:26:01 CST 2021 ;; MSG SIZE  rcvd: 237

NodePort类型的Service

在之前的样例中,创建的Service的IP地址只有集群内部可以访问,如果希望Service暴露给集群外部使用,那么就要使用到另外一种类型的Service,称为NodePort类型。NodePor的工作原理其实就是将service的端口映射到Node的一个端口上,然后就可以通过NodeIp:NodePort来访问service了。

k8s之Service详解-Service使用

创建service-nodeport.yaml,内容如下

apiVersion: v1
kind: Service
metadata:
name: service-nodeport
namespace: dev
spec:
selector:
app: nginx-pod
type: NodePort #service类型
ports:
- port: 80
nodePort: 30002 #指定绑定的node的端口(默认的取值范围是:30000-32767),如果不指定,会默认分配
targetPort: 80

使用配置文件

[root@master ~]# vim service-nodeport.yaml [root@master ~]# kubectl create -f service-nodeport.yaml  service/service-nodeport created [root@master ~]# kubectl get svc service-nodeport -n dev NAME               TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE service-nodeport   NodePort   10.103.29.82   <none>        80:30002/TCP   14s

通过电脑的浏览器对node进行访问,访问地址:master的主机ip加上30002端口

k8s之Service详解-Service使用

发现能够成功访问了

LoadBalancer类型的Service

LoadBalancer和NodePort很相似,目的都是向外部暴露一个端口,区别在于LoadBalancer会在集群的外部再来做一个负载均衡设备,而这个设备需要外部环境支持的,外部服务发送到这个设备上的请求,会被设备负载之后转发到集群中。

k8s之Service详解-Service使用

 

ExternalName类型的Service

ExternalName类型的Service用于引入集群外部的服务,它通过externalName属性指定外部一个服务的地址,然后在集群内部访问此Service就可以访问到外部的服务了

k8s之Service详解-Service使用

创建service-externalname.yaml,内容如下

apiVersion: v1 kind: Service metadata:   name: service-externalname   namespace: dev spec:   type: ExternalName  #service类型   externalName: www.baidu.com  #改成ip地址也可以

使用配置文件

[root@master ~]# vim service-externalname.yaml [root@master ~]# kubectl create -f service-externalname.yaml  service/service-externalname created [root@master ~]# kubectl get svc service-externalname -n dev NAME                   TYPE           CLUSTER-IP   EXTERNAL-IP     PORT(S)   AGE service-externalname   ExternalName   <none>       www.baidu.com   <none>    17s

域名解析

[root@master ~]# dig @10.96.0.10 service-externalname.dev.svc.cluster.local  ; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.5 <<>> @10.96.0.10 service-externalname.dev.svc.cluster.local ; (1 server found) ;; global options: +cmd ;; Got answer: ;; WARNING: .local is reserved for Multicast DNS ;; You are currently testing what happens when an mDNS query is leaked to DNS ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27636 ;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1 ;; WARNING: recursion requested but not available  ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags:; udp: 4096 ;; QUESTION SECTION: ;service-externalname.dev.svc.cluster.local. IN A  ;; ANSWER SECTION: service-externalname.dev.svc.cluster.local. 30 IN CNAME    www.baidu.com. www.baidu.com.        30    IN    CNAME    www.a.shifen.com. www.a.shifen.com.    30    IN    A    39.156.66.14 www.a.shifen.com.    30    IN    A    39.156.66.18  ;; Query time: 31 msec ;; SERVER: 10.96.0.10#53(10.96.0.10) ;; WHEN: 四 8月 12 11:58:31 CST 2021 ;; MSG SIZE  rcvd: 247

 

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