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Kubernetes之Service的使用

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导读：本篇文章讲解 Kubernetes之Service的使用，希望对大家有帮助，欢迎收藏，转发！站点地址：www.bmabk.com，来源：原文

Service概述

kubernetes提供了Service资源，Service对提供同一个服务的多个pod进行聚合，并且提供一个统一的入口地址。通过访问Service的入口地址就能访问到pod服务。

Service实现核心其实是kube-proxy服务进程，每个Node节点上都运行着一个kube-proxy服务进程。当创建Service的时候通过api-server向etcd写入创建的service信息，而kube-proxy会基于监听的机制发现Service的变动，然后将最新Service信息转换成对应的访问规则。

kube-proxy

kube-proxy支持三种工作模式: userspace模式、iptables模式、ipvs模式

userspace

kube-proxy为每一个Service创建一个监听端口，发向Cluster IP的请求被Iptables规则重定向到kube-proxy监听的端口上，kube-proxy根据LB算法选择一个提供服务的Pod并和其建立链接，以此将请求转发到Pod上。

kube-proxy充当一个四层负载均衡器角色。由于kube-proxy运行在userspace中，在进行转发处理时会增加内核和用户空间之间的数据拷贝，虽比较稳定，但效率比较低

iptables

kube-proxy为service对应的每个Pod创建对应的iptables规则，直接将发向Cluster IP的请求重定向到一个Pod IP。

kube-proxy不承担四层负载均衡器角色，只负责创建iptables规则。优点是较userspace模式效率更高，但不能提供灵活的LB策略，当后端Pod不可用时也无法进行重试

ipvs

​ ipvs模式和iptables类似，kube-proxy监控Pod的变化并创建相应的ipvs规则。ipvs相对iptables转发效率更高。除此以外，ipvs支持更多的LB算法。

Service类型

ClusterIP：默认值，它是Kubernetes系统自动分配的虚拟IP，只能在集群内部访问

NodePort：将Service通过指定的Node上的端口暴露给外部，通过此方法，就可以在集群外部访问服务

HeadLiness：不使用Service提供的负载均衡功能，通过自己来控制负载均衡策略

LoadBalancer：使用外接负载均衡器完成到服务的负载分发，此模式需要外部环境支持

ExternalName： 把集群外部的服务引入集群内部，直接使用

准备Deployment与Pod

准备Deployment

创建vim deployment-pod.yaml

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

准备Pod

# 创建Pod
[root@administrator k8s]# kubectl create -f  deployment-pod.yaml
deployment.apps/deployment-pod created

# 查看pod详情
[root@administrator k8s]# kubectl get pods -o wide --show-labels
NAME                              READY   STATUS    RESTARTS   AGE   IP            NODE            NOMINATED NODE   READINESS GATES   LABELS
deployment-pod-6c568d58df-4cj2c   1/1     Running   0          56s   172.17.0.10   administrator   <none>           <none>            app=nginx-pod,pod-template-hash=6c568d58df
deployment-pod-6c568d58df-bcxd5   1/1     Running   0          56s   172.17.0.8    administrator   <none>           <none>            app=nginx-pod,pod-template-hash=6c568d58df
deployment-pod-6c568d58df-krnqb   1/1     Running   0          56s   172.17.0.9    administrator   <none>           <none>            app=nginx-pod,pod-template-hash=6c568d58df

# 访问测试
[root@administrator k8s]# curl 172.17.0.10
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

ClusterIP类型

创建Service

创建vim service-clusterip.yaml

apiVersion: v1
kind: Service
metadata:
  name: service-clusterip
  namespace: default
spec:
  selector:
    app: nginx-pod
  clusterIP: # 虚拟服务的ip地址、service的ip地址，如果不写，默认生成一个
  type: ClusterIP # Service类型，指定service的访问方式
  ports:
  - port: 80  # Service端口       
    targetPort: 80 # pod端口   

# 创建service
[root@administrator k8s]# kubectl create -f service-clusterip.yaml
service/service-clusterip created

# 查看service
[root@administrator k8s]# kubectl get svc  -o wide
NAME                TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)   AGE   SELECTOR
kubernetes          ClusterIP   10.96.0.1      <none>        443/TCP   51m   <none>
service-clusterip   ClusterIP   10.107.13.81   <none>        80/TCP    37s   app=nginx-pod

# 查看service的详细信息
# Endpoints列表:当前service可以负载到的服务入口
[root@administrator k8s]# kubectl describe svc service-clusterip
Name:              service-clusterip
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=nginx-pod
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.107.13.81
IPs:               10.107.13.81
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         172.17.0.10:80,172.17.0.8:80,172.17.0.9:80
Session Affinity:  None
Events:            <none>

测试Service

可进入pod中的容器: kubectl exec -it deployment-pod-6c568d58df-4cj2c /bin/sh  

修改nginx的首页: echo "deployment-pod-6c568d58df-4cj2c" > /usr/share/nginx/html/index.html

[root@administrator k8s]# curl 10.107.13.81:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Endpoint

Endpoint是kubernetes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selector描述产生的。

[root@administrator k8s]# kubectl get endpoints -o wide
NAME                ENDPOINTS                                    AGE
kubernetes          172.22.4.21:8443                             58m
service-clusterip   172.17.0.10:80,172.17.0.8:80,172.17.0.9:80   7m19s

负载分发策略

对Service请求，就会将请求分发到Pod上去。kubernetes提供了两种负载分发策略：

1.如果不定义，默认使用kube-proxy的策略，比如随机、轮询

2.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固定的一个Pod上。

第二种负载分发策略需要在spec中添加sessionAffinity:ClientIP

spec:
  sessionAffinity:ClientIP # session亲和性，支持ClientIP、None两个选项
  selector:
    app: nginx-pod
  clusterIP: # service的ip地址，如果不写，默认生成一个

NodePort类型

NodePort类型的Service用于将Service暴露给集群外部使用

工作原理：将service的端口映射到Node主机的一个端口上，然后通过NodeIp:NodePort来访问service

创建Service

创建service-nodeport.yaml

apiVersion: v1
kind: Service
metadata:
  name: service-nodeport
  namespace: default
spec:
  selector:
    app: nginx-pod
  type: NodePort # service类型
  ports:
  - port: 80
    nodePort: 30001 # 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    

# 创建service
[root@administrator k8s]#  kubectl create -f service-nodeport.yaml
service/service-nodeport created

# 查看service
[root@administrator k8s]# kubectl get svc -o wide
NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE   SELECTOR
kubernetes           ClusterIP   10.96.0.1       <none>        443/TCP        94m   <none>
service-clusterip    ClusterIP   10.107.13.81    <none>        80/TCP         43m   app=nginx-pod
service-headliness   ClusterIP   None            <none>        80/TCP         16m   app=nginx-pod
service-nodeport     NodePort    10.98.112.245   <none>        80:30001/TCP   11s   app=nginx-pod

测试Service

[root@administrator k8s]# curl 127.0.0.1:30001
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

HeadLiness类型

若不想使用Service提供的负载均衡功能，而希望自己控制负载均衡策略，则可以使用HeadLiness。

kubernetes提供了HeadLiness Service，这类Service不会分配Cluster IP，如果想要访问service，只能通过service的域名进行查询。

创建Service

创建vim service-headliness.yaml

apiVersion: v1
kind: Service
metadata:
  name: service-headliness
  namespace: default
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

# 创建service
[root@administrator k8s]# kubectl create -f service-headliness.yaml
service/service-headliness created

# 获取service,CLUSTER-IP未分配IP
[root@administrator k8s]# kubectl get svc service-headliness  -o wide
NAME                 TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE   SELECTOR
service-headliness   ClusterIP   None         <none>        80/TCP    17s   app=nginx-pod

# 查看service详情
[root@administrator k8s]# kubectl describe svc service-headliness
Name:              service-headliness
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=nginx-pod
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                None
IPs:               None
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         172.17.0.10:80,172.17.0.8:80,172.17.0.9:80
Session Affinity:  None
Events:            <none>

查看域名的解析

进入容器，查看域名的解析情况

[root@administrator k8s]#  kubectl exec -it deployment-pod-6c568d58df-4cj2c /bin/bash
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
root@deployment-pod-6c568d58df-4cj2c:/# cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

测试Service

安装dig

dig用于从DNS域名服务器上获取主机地址信息

yum install bind-utils

[root@administrator ~]# dig @10.96.0.10 service-headliness.default.svc.cluster.local

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.9 <<>> @10.96.0.10 service-headliness.default.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: 15791
;; 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.default.svc.cluster.local. IN A

;; ANSWER SECTION:
service-headliness.default.svc.cluster.local. 30 IN A 172.17.0.8
service-headliness.default.svc.cluster.local. 30 IN A 172.17.0.10
service-headliness.default.svc.cluster.local. 30 IN A 172.17.0.9

;; Query time: 17 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Thu Mar 31 22:13:57 CST 2022
;; MSG SIZE  rcvd: 253

LoadBalancer类型

LoadBalancer类型的Service用于向外部暴露一个端口，相比NodePort类型Service而言，LoadBalancer会在集群外部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

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

创建vim service-externalname.yaml

apiVersion: v1
kind: Service
metadata:
  name: service-externalname
  namespace: default
spec:
  type: ExternalName # service类型
  externalName: www.baidu.com  # 域名或IP

# 创建service
[root@administrator k8s]# kubectl  create -f service-externalname.yaml
service/service-externalname created

# 查看service
[root@administrator k8s]# kubectl describe svc service-externalname
Name:              service-externalname
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          <none>
Type:              ExternalName
IP Families:       <none>
IP:
IPs:               <none>
External Name:     www.baidu.com
Session Affinity:  None
Events:            <none>

测试Service

# 进入容器，查看域名的解析情况
[root@administrator k8s]# kubectl exec -it deployment-pod-6c568d58df-4cj2c /bin/bash
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl exec [POD] -- [COMMAND] instead.
root@deployment-pod-6c568d58df-4cj2c:/# cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

# 域名解析
[root@administrator ~]# dig @10.96.0.10 service-externalname.default.svc.cluster.local

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.9 <<>> @10.96.0.10 service-externalname.default.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: 14408
;; 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.default.svc.cluster.local.        IN A

;; ANSWER SECTION:
service-externalname.default.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       14.215.177.38
www.a.shifen.com.       30      IN      A       14.215.177.39

;; Query time: 14 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Thu Mar 31 22:31:15 CST 2022
;; MSG SIZE  rcvd: 255

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