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 <string>
kind <string>
metadata <Object>
spec <Object>
status <Object>
kubectl explain Service.spec
allocateLoadBalancerNodePorts <boolean>#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 <string> #service的虚拟ip地址
externalIPs <[]string> #公开到集群外的ip
externalName <string> #指定外部dns名称
externalTrafficPolicy <string> #定义外部流量策略，可选cluster或local
healthCheckNodePort <integer> #用于健康检查的端口
sessionAffinity <string> #会话策略，可选ClientIP或者None
type <string> #类型，有四种，ExternalName, ClusterIP, NodePort, LoadBalancer
ports <[]Object>
kubectl explain service.spec.ports
name <string>
nodePort <integer> #对外映射的端口
port <integer> -required- #service的端口
protocol <string> #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 <none> 443/TCP 12d
service ClusterIP 10.107.178.176 <none> 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
<!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>
#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 <none> 443/TCP 12d
service NodePort 10.108.9.134 <none> 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
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
<!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>
#清理
kubectl delete -f service-externalname.yaml
kubectl delete -f service-in-server.yaml
kubectl delete -f pod-in-server.yaml