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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

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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
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使用配置文件

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[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>
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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）

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#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
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ClusterIp类型的Service

创建service-clusterip.yaml文件

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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
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 使用配置文件

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[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
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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。

[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
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#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
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修改分发策略为sessionAffinity:ClientIP

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#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>
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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

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[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
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再次进行循环访问测试，发现这次只访问一个pod

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[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
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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

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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
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使用配置文件

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[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>
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查看域名解析情况

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[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
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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。

创建service-nodeport.yaml，内容如下

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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
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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

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。

 

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

创建service-externalname.yaml，内容如下

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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
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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

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[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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 出处：https://www.cnblogs.com/Ayanamidesu/p/15122969.html

 

 


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