k8s中Service负载均衡和Service类型介绍

树下一少年2023-12-03 13:11

目录

一.service介绍

二.service参数详解

三.定义service的两种方式

1.命令行expose

2.yaml文件

四.service负载均衡配置

1.kube-proxy代理模式

（1）设置ipvs

（2）负载均衡调度策略

2.会话保持

3.案例演示

五.四种Service类型

1.clusterip

2.NodePort

3.LoadBalancer

（1）先在集群master上开启kube-proxy的strictARP，来使所有网卡停止响应其他网卡请求，以openelb来替代。

（2）应用下载openelb.yaml（需要修改镜像地址）

（3）编写yaml文件来添加eip地址池

（4）创建service来验证

4.ExternalName

一.service介绍

之前我们讲到的pod创建，里面有服务需要被集群内部访问或被外界访问，这样情况我们就需要借助service来为应用提供统一入口地址，他主要提供网络服务，将请求按负载均衡算法分发到各个容器。在访问时，pod的IP地址时会变化的，显然在pod提供稳定服务时不能通过IP地址去访问。

二.service参数详解

apiVersion: v1  #必写
kind: Service   #必写
metadata:    #必写
  annotations:   #自定义的注解属性列表
    kubectl.kubernetes.io/last-applied-configuration: |
      {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"my-nginx","namespace":"myns"},"spec":{"ports":[{"port":80,"protocol":"TCP","targetPort":80}],"selector":{"name":"my-nginx"}}}
  creationTimestamp: "2023-12-02T01:18:01Z"
  name: my-nginx   #必写
  namespace: myns   #必写，建议和你创建pod和pod控制器的名称空间一致
  resourceVersion: "1537"
  uid: ab1bb8ce-be87-48d4-8396-5e802dfbca8c
spec:   #必写
  clusterIP: 10.109.39.11  #虚拟IP，当type=ClusterIP时设置，可以自己指定，也可以不写等系统自己分配
  clusterIPs:
  - 10.109.39.11
  internalTrafficPolicy: Cluster
  ipFamilies:
  - IPv4
  ipFamilyPolicy: SingleStack
  ports:   #端口暴露情况
  - port: 80  #服务监听的端口
    protocol: TCP  #端口协议，默认TCP，支持TCP/UDP
    targetPort: 80  #转发到后端pod的端口
    nodePort: number   #type=NodePort时设置，映射到主机的端口，可以自己指定也可以不写等系统分配，设置了type=NodePort，其他节点和外界就可以通过"此主机地址+这个端口号"进行访问
  selector:   #选择器，必写
    name: my-nginx  #注意一致性
  sessionAffinity: None  #是否支持session，默认none，也可以填写ClientIP,表示根据客户端IP来将同一个客户端请求分配到同一个pod
  type: ClusterIP  #类型选择，ClusterIP、NodePort、LoadBalancer，后面会详细介绍
status:   #当type=LoadBalancer时这只，设置外部负载均衡器的地址（公有云环境），后面演示的时候介绍
  loadBalancer: {}

三.定义service的两种方式

1.命令行expose

这里创建一个关于nginx服务的3个副本数的pod，并且使用expose方式为其创建service，其中，--port=80指定nginx服务监听端口，--type=ClusterIP指定类型， --target-port=80指定转发到后端某端口，并使用暴露出来的IP进行访问验证是否成功。

[root@k8s-master service]# cat service1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx
  template:
    metadata:
      labels:
        name: my-nginx
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
[root@k8s-master service]# kubectl get pods -n myns
NAME                       READY   STATUS    RESTARTS   AGE
my-nginx-7c787d8bb-g6fb5   1/1     Running   0          9s
my-nginx-7c787d8bb-t5jdh   1/1     Running   0          9s
my-nginx-7c787d8bb-znd22   1/1     Running   0          9s
[root@k8s-master service]# kubectl get deploy -n myns
NAME       READY   UP-TO-DATE   AVAILABLE   AGE
my-nginx   3/3     3            3           15s
​
[root@k8s-master service]# kubectl expose deployment my-nginx -n myns --port=80 --type=ClusterIP --target-port=80 
service/my-nginx exposed
[root@k8s-master service]# kubectl get service -n myns  #使用下方IP进行访问
NAME       TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE
my-nginx   ClusterIP   10.111.4.81   <none>        80/TCP    6s
​
[root@k8s-master service]# curl 10.111.4.81
<!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>
​
[root@k8s-node1 ~]# curl 10.111.4.81   #在node1上访问，验证ClusterIP集群内部访问是否成功
<!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>

2.yaml文件

这里在上面的deployment基础上继续配置service，ports部分和selector部分显得尤为重要，具体看代码注释

[root@k8s-master service]# cat service1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
spec:
  ports:   
  - protocol: TCP   #TCP协议
    targetPort: 80    #转发到后端pod的80端口
    port: 80   #服务监听80端口
  selector:   #与deploy上面的模板进行匹配，表示为标签为name: my-nginx-deploy的pod开放服务
    name: my-nginx-deploy        
​
[root@k8s-master service]# kubectl apply -f service1.yaml 
deployment.apps/my-nginx created
service/my-nginx-service created
[root@k8s-master service]# kubectl get service -n myns
NAME               TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE
my-nginx-service   ClusterIP   10.98.64.75   <none>        80/TCP    7s
[root@k8s-master service]# curl 10.98.64.75
<!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>

四.service负载均衡配置

1.kube-proxy代理模式

这里主要介绍ipvs代理，他实现从service到后端endpoint的负载分发任务，相较于旧版本的userspace和iptables来讲，ipvs具有更高的转发效率和吞吐率，也支持更多的负载均衡策略接下来介绍如何开启ipvs（之前介绍label那篇文章也讲到过），若不开启，会自动切换到iptables。

（1）设置ipvs

[root@k8s-master service]# lsmod | grep ip_vs   #加载查看内核模块
ip_vs_sh               12688  0 
ip_vs_wrr              12697  0 
ip_vs_rr               12600  0 
ip_vs                 145458  6 ip_vs_rr,ip_vs_sh,ip_vs_wrr
nf_conntrack          139264  10 ip_vs,nf_nat,nf_nat_ipv4,nf_nat_ipv6,xt_conntrack,nf_nat_masquerade_ipv4,nf_nat_masquerade_ipv6,nf_conntrack_netlink,nf_conntrack_ipv4,nf_conntrack_ipv6
libcrc32c              12644  4 xfs,ip_vs,nf_nat,nf_conntrack
​
#将node部分改为ipvs
[root@k8s-master service]# kubectl edit configmap kube-proxy -n kube-system 
configmap/kube-proxy edited
"
metricsBindAddress: ""
    mode: "ipvs"
    nodePortAddresses: null
    oomScoreAdj: null
"
​
#删除kube-proxy的pod，自动重新拉取
[root@k8s-master service]# kubectl get pods -n kube-system | grep kube-proxy
kube-proxy-95q7f                           1/1     Running   0          94m
kube-proxy-qf7wh                           1/1     Running   0          92m
kube-proxy-rtg5c                           1/1     Running   0          92m
[root@k8s-master service]# kubectl delete pod kube-proxy-95q7f kube-proxy-qf7wh kube-proxy-rtg5c -n kube-system 
pod "kube-proxy-95q7f" deleted
pod "kube-proxy-qf7wh" deleted
pod "kube-proxy-rtg5c" deleted
[root@k8s-master service]# kubectl get pods -n kube-system | grep kube-proxy
kube-proxy-7b5fc                           1/1     Running   0          6s
kube-proxy-pvv6k                           1/1     Running   0          6s
kube-proxy-vbfnd                           1/1     Running   0          6s
​
#验证生效
[root@k8s-master service]# kubectl logs kube-proxy-7b5fc -n kube-system | grep ipvs
I1202 02:44:06.831781       1 server_others.go:218] "Using ipvs Proxier"
[root@k8s-master service]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  192.168.2.150:30572 rr
  -> 10.244.36.75:80              Masq    1      0          0         
  -> 10.244.169.147:80            Masq    1      0          0         
  -> 10.244.169.148:80            Masq    1      0          0         
TCP  10.96.0.1:443 rr
  -> 192.168.2.150:6443           Masq    1      1          0         
TCP  10.96.0.10:53 rr
  -> 10.244.235.193:53            Masq    1      0          0         
  -> 10.244.235.194:53            Masq    1      0          0         
TCP  10.96.0.10:9153 rr
  -> 10.244.235.193:9153          Masq    1      0          0         
  -> 10.244.235.194:9153          Masq    1      0          0         
TCP  10.98.197.131:80 rr
  -> 10.244.36.75:80              Masq    1      0          0         
  -> 10.244.169.147:80            Masq    1      0          0         
  -> 10.244.169.148:80            Masq    1      0          0         
TCP  10.244.235.192:30572 rr
  -> 10.244.36.75:80              Masq    1      0          0         
  -> 10.244.169.147:80            Masq    1      0          0         
  -> 10.244.169.148:80            Masq    1      0          0         
UDP  10.96.0.10:53 rr
  -> 10.244.235.193:53            Masq    1      0          0         
  -> 10.244.235.194:53            Masq    1      0          0

（2）负载均衡调度策略

rr（Round Robin）：轮询算法，将请求按照顺序依次分发给后端服务器。每个请求都按照先后顺序分配给下一个服务器，直到所有服务器都被分配到一个请求。然后再从头开始循环。

lc（Least Connections）：最小连接数算法，将请求分发给当前连接数最少的服务器。通过监视服务器上的活动连接数并选择最少连接的服务器，可以实现负载均衡。

dh（Destination Hashing）：目标哈希算法，根据请求的特定目标信息（例如源 IP 地址或会话 ID）计算哈希值，并将请求分发给与哈希值匹配的服务器。这样可以确保相同的请求始终被分发到相同的服务器上。

sh（Source Hashing）：源哈希算法，类似于目标哈希算法，但是使用源 IP 地址而不是目标信息来计算哈希值。这样可以确保来自同一来源的请求始终被发送到同一台服务器。

sed（Shortest Expected Delay）：最短期望延迟算法，根据每个服务器的预计延迟时间来选择服务器。该算法会考虑服务器的负载和延迟，并选择具有最短预计延迟的服务器来处理请求。

nq（Nginx Queue）：Nginx 队列算法(永不排队)，将请求放入队列中，并按照特定规则进行调度。这种算法通常与 Nginx 反向代理服务器一起使用，可以根据不同的规则（例如权重、连接数等）进行请求调度。

2.会话保持

通过sessionAffinity设置首次将客户端发起的请求发送某pod，之后的该客户端的请求都发往此pod，同时还可以配置timeoutSeconds:为其设置会话保持时间，详情见案例演示。

3.案例演示

没设置会话保持时，自动按照算法按照调度给3个pod（pod配置不同的页面以方面验证）

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    name: my-nginx-deploy
  type: ClusterIP
​
[root@k8s-master service]# curl 10.107.18.89
pod3
[root@k8s-master service]# curl 10.107.18.89
pod2
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod3
[root@k8s-master service]# curl 10.107.18.89
pod2

配置会话保持

[root@k8s-master service]# cat service1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
spec:
  sessionAffinity: ClientIP
  sessionAffinityConfig:
    clientIP:
      timeoutSeconds: 10
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    name: my-nginx-deploy
  type: ClusterIP
​
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1
[root@k8s-master service]# curl 10.107.18.89
pod1

五.四种Service类型

1.clusterip

上面已经讲到clusterip是集群内部访问类型，并且已经演示，接下来介绍其他类型

2.NodePort

这个类型使得服务不仅可以被集群内部访问，还可以被集群外部访问，nodeport暴露的是TCP4层，但会对集群节点主机端口产生占用，不适合大规模使用。需要注意的是：指定了类型为nodeport后，指定或自定暴露出来的端口的node的port（主机port），那么集群外部访问就需要使用node的ip（主机ip）+ node的port去访问。若是指定端口，应保持在30000-32767这个范围内。

[root@k8s-master service]# cat service1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
    nodePort: 30572  #指定暴露node上的端口
  selector:
    name: my-nginx-deploy 
  type: NodePort  #指定类型
​
[root@k8s-master service]# kubectl apply -f service1.yaml 
deployment.apps/my-nginx unchanged
service/my-nginx-service created
[root@k8s-master service]# kubectl get service -n myns
NAME               TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
my-nginx-service   NodePort   10.98.197.131   <none>        80:30572/TCP   9s
​
#如下，集群内部同样可以使用clusterip进行访问
[root@k8s-node1 ~]# curl 10.98.197.131
<!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>

如下图，集群外部要使用主机地址+该端口进行访问

3.LoadBalancer

LoadBalancer类型专属于云服务，可以动态分配网关，这里介绍主要介绍openelb。

OpenELB是一个开源的企业级负载均衡器，它为 Kubernetes 集群提供了强大的负载均衡功能。OpenELB 通过与 Kubernetes API 交互来获取服务和端点信息，并与 Kubernetes的内部组件（如 etcd）进行通信，以获取集群状态信息。这使得 OpenELB 能够动态地感知到整个集群的状态和服务变化。他可以根据 Kubernetes 中服务和端点的变化动态地更新负载均衡策略，确保流量能够按照需求正确地路由到后端 Pod。接下来讲述如何部署openelb

（1）先在集群master上开启kube-proxy的strictARP，来使所有网卡停止响应其他网卡请求，以openelb来替代。

[root@k8s-master service]# kubectl edit configmap kube-proxy -n kube-system
#将strictARP改为true

（2）应用下载openelb.yaml（需要修改镜像地址）

这里的文件已经修改好了的，一般是需要将1267和1300行两处的image地址更改（kubespheredev/kube-webhook-certgen:v1.1.1）

链接：百度网盘 请输入提取码 提取码：df6b

[root@k8s-master service]# kubectl apply -f openelb.yaml
[root@k8s-master service]# kubectl get pods -n openelb-system
NAME                              READY   STATUS      RESTARTS   AGE
openelb-admission-create-g4q5f    0/1     Completed   0          17s
openelb-admission-patch-j679s     0/1     Completed   0          17s
openelb-keepalive-vip-jk5lh       1/1     Running     0          8s
openelb-keepalive-vip-xcjpw       1/1     Running     0          8s
openelb-manager-99b49789c-ssn4x   1/1     Running     0          17s

（3）编写yaml文件来添加eip地址池

[root@k8s-master service]# vim ip-pool.yaml
apiVersion: network.kubesphere.io/v1alpha2   #版本可以在成功应用openelb之后使用kubectl explain Eip.apiVersion来查看
kind: Eip
metadata:
  name: my-eip-pool
spec:
  address: 192.168.2.11-192.168.2.20    #写一段没有使用的IP地址范围作为ip-pool，要与主机位于同一网段
  protocol: layer2
  disable: false
  interface: ens33   #指定主机网卡名称
​
[root@k8s-master service]# kubectl apply -f ip-pool.yaml 
eip.network.kubesphere.io/my-eip-pool created
[root@k8s-master service]# kubectl get eip
NAME          CIDR                        USAGE   TOTAL
my-eip-pool   192.168.2.11-192.168.2.20           10

（4）创建service来验证

复制代码 
​
[root@k8s-master service]# cat service1.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
  annotations:   #这三行详情也要添加，尤为重要
    lb.kubesphere.io/v1alpha1: openelb
    protocol.openelb.kubesphere.io/v1alpha1: layer2  
    eip.openelb.kubesphere.io/v1alpha2: my-eip-pool   #指定创建地址池时指定的名称
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    name: my-nginx-deploy
  type: LoadBalancer   #指定type为LoadBalancer
​
[root@k8s-master service]# kubectl apply -f  service1.yaml 
deployment.apps/my-nginx created
service/my-nginx-service created
[root@k8s-master service]# kubectl get service my-nginx-service -n myns  #验证时访问192.168.2.11即可
NAME               TYPE           CLUSTER-IP      EXTERNAL-IP    PORT(S)        AGE
my-nginx-service   LoadBalancer   10.107.18.126   192.168.2.11   80:30921/TCP   20s
​
[root@k8s-master service]# curl 192.168.2.11
<!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>
[root@k8s-master service]# kubectl get pods -n myns
NAME                        READY   STATUS    RESTARTS   AGE
my-nginx-5d67c8f488-bvvcm   1/1     Running   0          64s
my-nginx-5d67c8f488-cf9vd   1/1     Running   0          64s
my-nginx-5d67c8f488-jrhgt   1/1     Running   0          64s
[root@k8s-master service]# kubectl exec -it my-nginx-5d67c8f488-bvvcm -n myns -- /bin/sh -c "echo pod1 > /usr/share/nginx/html/index.html"
[root@k8s-master service]# kubectl exec -it my-nginx-5d67c8f488-cf9vd -n myns -- /bin/sh -c "echo pod2 > /usr/share/nginx/html/index.html"
[root@k8s-master service]# kubectl exec -it my-nginx-5d67c8f488-jrhgt -n myns -- /bin/sh -c "echo pod3 > /usr/share/nginx/html/index.html"
[root@k8s-master service]# curl 192.168.2.11
pod2
[root@k8s-master service]# curl 192.168.2.11
pod1
[root@k8s-master service]# curl 192.168.2.11
pod1
[root@k8s-master service]# curl 192.168.2.11
pod3

4.ExternalName

它允许将 Kubernetes 集群内部的服务映射到集群外部的服务地址。这种服务类型通常用于需要访问集群外部服务的情况，在 Pod 内部，你可以通过该 Service 的名称来进行访问，Kubernetes 会负责将请求路由到外部服务地址

[root@k8s-master service]# cat service2.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    name: my-nginx
  name: my-nginx
  namespace: myns
spec:
  replicas: 3
  selector:
    matchLabels:
      name: my-nginx-deploy
  template:
    metadata:
      labels:
        name: my-nginx-deploy
    spec:
      containers:
      - name: my-nginx-pod
        image: nginx
        ports:
        - containerPort: 80
​
---
​
apiVersion: v1
kind: Service
metadata:
  name: my-nginx-service
  namespace: myns
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    name: my-nginx-deploy
  type: ExternalName   #指定类型为ExternalName
  externalName: www.baidu.com   #要访问的外部地址，可以是域名、IP等
​
[root@k8s-master service]# kubectl get pods -n myns
NAME                        READY   STATUS    RESTARTS   AGE
my-nginx-5d67c8f488-48dsc   1/1     Running   0          19m
my-nginx-5d67c8f488-mn9qt   1/1     Running   0          19m
my-nginx-5d67c8f488-xgbgw   1/1     Running   0          19m
​
# nslookup my-nginx-service
Server:     10.96.0.10
Address:    10.96.0.10#53
my-nginx-service.myns.svc.cluster.local canonical name = www.baidu.com.
Name:   www.baidu.com
Address: 39.156.66.14
Name:   www.baidu.com
Address: 39.156.66.18
Name:   www.baidu.com
Address: 2409:8c00:6c21:104f:0:ff:b03f:3ae
Name:   www.baidu.com
Address: 2409:8c00:6c21:1051:0:ff:b0af:279a
# ping my-nginx-service
PING www.baidu.com (39.156.66.18): 56 data bytes
64 bytes from 39.156.66.18: icmp_seq=0 ttl=127 time=43.167 ms
64 bytes from 39.156.66.18: icmp_seq=1 ttl=127 time=147.273 ms
64 bytes from 39.156.66.18: icmp_seq=2 ttl=127 time=53.310 ms
^C--- www.baidu.com ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 43.167/81.250/147.273/46.869 ms
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